Fix build warning and other small fixes

Fixes these build warnings:

session.c:621:21: warning: variable 'wm_command_count' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
                if (client_id)
                    ^~~~~~~~~
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:621:17: note: remove the 'if' if its condition is always false
                if (client_id)
                ^~~~~~~~~~~~~~
session.c:616:17: warning: variable 'wm_command_count' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
            if (xstreq (c->class.res_name, m->res_name)
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:570:21: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                    ^
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:616:13: note: remove the 'if' if its condition is always true
            if (xstreq (c->class.res_name, m->res_name)
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:619:32: warning: variable 'wm_command_count' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
                    || xstreq (c->name, m->wm_name)))
                       ~~~~~~~~^~~~~~~~~~~~~~~~~~~~
session.c:570:37: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                                    ^~~~~~
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:619:32: note: remove the '&&' if its condition is always true
                    || xstreq (c->name, m->wm_name)))
                               ^
session.c:619:32: warning: variable 'wm_command_count' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
                    || xstreq (c->name, m->wm_name)))
                               ^~~~~~~
session.c:570:37: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                                    ^
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:619:32: note: remove the '&&' if its condition is always true
                    || xstreq (c->name, m->wm_name)))
                               ^
session.c:616:17: warning: variable 'wm_command_count' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
            if (xstreq (c->class.res_name, m->res_name)
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:570:21: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:616:17: note: remove the '&&' if its condition is always true
            if (xstreq (c->class.res_name, m->res_name)
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:570:21: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                    ^
session.c:616:25: warning: variable 'wm_command_count' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
            if (xstreq (c->class.res_name, m->res_name)
                ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:570:37: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                                    ^~~~~~
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:616:25: note: remove the '&&' if its condition is always true
            if (xstreq (c->class.res_name, m->res_name)
                        ^
session.c:616:25: warning: variable 'wm_command_count' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
            if (xstreq (c->class.res_name, m->res_name)
                        ^~~~~~~~~~~~~~~~~
session.c:570:37: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                                    ^
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:616:25: note: remove the '&&' if its condition is always true
            if (xstreq (c->class.res_name, m->res_name)
                        ^
session.c:605:13: warning: variable 'wm_command_count' is used uninitialized whenever 'if' condition is true [-Wsometimes-uninitialized]
        if ((window_role) || (m->window_role))
            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:605:9: note: remove the 'if' if its condition is always false
        if ((window_role) || (m->window_role))
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:605:13: warning: variable 'wm_command_count' is used uninitialized whenever '||' condition is true [-Wsometimes-uninitialized]
        if ((window_role) || (m->window_role))
            ^~~~~~~~~~~~~
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:605:13: note: remove the '||' if its condition is always false
        if ((window_role) || (m->window_role))
            ^~~~~~~~~~~~~~~~
session.c:594:9: warning: variable 'wm_command_count' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
    if (xstreq (client_id, m->client_id))
        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:570:21: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:594:5: note: remove the 'if' if its condition is always true
    if (xstreq (client_id, m->client_id))
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
session.c:594:17: warning: variable 'wm_command_count' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
    if (xstreq (client_id, m->client_id))
        ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
session.c:570:37: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                                    ^~~~~~
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:594:17: note: remove the '&&' if its condition is always true
    if (xstreq (client_id, m->client_id))
                ^
session.c:594:17: warning: variable 'wm_command_count' is used uninitialized whenever '&&' condition is false [-Wsometimes-uninitialized]
    if (xstreq (client_id, m->client_id))
                ^~~~~~~~~
session.c:570:37: note: expanded from macro 'xstreq'
#define xstreq(a,b) ((!a && !b) || (a && b && (strcmp(a,b)==0)))
                                    ^
session.c:680:10: note: uninitialized use occurs here
    if ((wm_command_count > 0) && (wm_command))
         ^~~~~~~~~~~~~~~~
session.c:594:17: note: remove the '&&' if its condition is always true
    if (xstreq (client_id, m->client_id))
                ^
session.c:580:26: note: initialize the variable 'wm_command_count' to silence this warning
    gint wm_command_count;
                         ^
                          = 0

And other small fixes.