exo-open: Fix GOptionContext memory leak
This MR fixes the following leak:
Direct leak of 88 byte(s) in 1 object(s) allocated from:
#0 0x5c2b37b61f79 in calloc (/usr/local/bin/exo-open+0x15df79) (BuildId: beebbfb10777b984)
#1 0x76e0711482c2 in g_malloc0 /usr/src/debug/glib2/build/../glib/glib/gmem.c:133:13
#2 0x76e071148318 in g_option_context_new /usr/src/debug/glib2/build/../glib/glib/goption.c:208:13
#3 0x5c2b37baa712 in main /home/s/code/exo/exo-open/main.c:628:13
#4 0x76e070da7c87 in __libc_start_call_main /usr/src/debug/glibc/glibc/csu/../sysdeps/nptl/libc_start_call_main.h:58:16
#5 0x76e070da7d4b in __libc_start_main /usr/src/debug/glibc/glibc/csu/../csu/libc-start.c:360:3
#6 0x5c2b37a75b54 in _start (/usr/local/bin/exo-open+0x71b54) (BuildId: beebbfb10777b984)
I noticed the leak while using the "Open Terminal Here" menu item in Thunar.