manager: Fix SmsClientHostName leak

Leak report

161 bytes in 7 blocks are definitely lost in loss record 9,577 of 10,628
   at 0x48447A8: malloc (vg_replace_malloc.c:446)
   by 0x5897716: _IceTransGetPeerNetworkId (Xtransutil.c:402)
   by 0x12D0C7: xfsm_manager_register_client (xfsm-manager.c:1024)
   by 0x13424E: sm_register_client (sm-layer.c:221)
   by 0x58ADA42: _SmsProcessMessage (sm_process.c:624)
   by 0x589E304: IceProcessMessages (process.c:378)
   by 0x133150: ice_process_messages (ice-layer.c:113)
   by 0x57A0EA2: g_io_unix_dispatch (giounix.c:170)
   by 0x57487BB: g_main_dispatch (gmain.c:3357)
   by 0x574B190: g_main_context_dispatch_unlocked (gmain.c:4208)
   by 0x574B190: g_main_context_iterate_unlocked (gmain.c:4273)
   by 0x574BA42: g_main_loop_run (gmain.c:4475)
   by 0x4CB10A6: gtk_main (gtkmain.c:1329)
   by 0x1244F6: main (main.c:398)

Docs

• https://www.x.org/releases/current/doc/libSM/SMlib.html#SmsClientHostName

Testing

• No issues were detected when testing the patch with Valgrind