im-status: Return if the dbus callback has been cancelled
To reproduce - when plugin is toggled in preferences.
(gdb) bt
#0 0x00007f26ed9b1704 in got_proxy_cb (source_object=<optimized out>, res=<optimized out>, pi=pi@entry=0x5592e8e13db0) at ../src/plugins/im-status/totem-im-status.c:124
#1 0x00007f2717905379 in g_task_return_now (task=task@entry=0x5592e8ea5810 [GTask]) at ../../../gio/gtask.c:1215
#2 0x00007f27179053b9 in complete_in_idle_cb (task=0x5592e8ea5810) at ../../../gio/gtask.c:1229
#3 0x00007f2717a83d6f in g_main_dispatch (context=0x5592e79efd20) at ../../../glib/gmain.c:3325
#4 g_main_context_dispatch (context=0x5592e79efd20) at ../../../glib/gmain.c:4043
#5 0x00007f2717a84118 in g_main_context_iterate (context=context@entry=0x5592e79efd20, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../../../glib/gmain.c:4119
#6 0x00007f2717a841cf in g_main_context_iteration (context=context@entry=0x5592e79efd20, may_block=may_block@entry=1) at ../../../glib/gmain.c:4184
#7 0x00007f2717933545 in g_application_run (application=0x5592e79c8100 [TotemObject], argc=-836459212, argc@entry=1, argv=argv@entry=0x7ffece24a6a8) at ../../../gio/gapplication.c:2559
#8 0x00005592e60d527b in main (argc=<optimized out>, argv=<optimized out>) at ../src/totem.c:83