This fixes this leak:
==21491== 384 (40 direct, 344 indirect) bytes in 1 blocks are definitely lost in loss record 18,518 of 19,643
==21491== at 0x8792D3A: g_type_create_instance (gtype.c:1848)
==21491== by 0x8779AC5: g_object_new_internal (gobject.c:1774)
==21491== by 0x8779FD4: g_object_newv (gobject.c:1921)
==21491== by 0x8779676: g_object_new (gobject.c:1614)
==21491== by 0x747DFFC: gtk_list_store_new (gtkliststore.c:424)
==21491== by 0x49C781: goa_panel_add_account_dialog_init (cc-online-accounts-add-account-dialog.c:300)
==21491== by 0x8792E7D: g_type_create_instance (gtype.c:1870)
==21491== by 0x8779AC5: g_object_new_internal (gobject.c:1774)
==21491== by 0x877A71A: g_object_new_valist (gobject.c:2033)
==21491== by 0x87796C5: g_object_new (gobject.c:1617)
==21491== by 0x49CC26: goa_panel_add_account_dialog_new (cc-online-accounts-add-account-dialog.c:380)
==21491== by 0x49B162: get_all_providers_cb (cc-online-accounts-panel.c:701)
==21491== by 0x8426107: g_simple_async_result_complete (gsimpleasyncresult.c:801)
==21491== by 0x8426153: complete_in_idle_cb (gsimpleasyncresult.c:813)
==21491== by 0x8A0C470: g_idle_dispatch (gmain.c:5397)
==21491== by 0x8A09AB8: g_main_dispatch (gmain.c:3122)
==21491== by 0x8A0A8FC: g_main_context_dispatch (gmain.c:3737)
==21491== by 0x8A0AAE0: g_main_context_iterate (gmain.c:3808)
==21491== by 0x8A0ABA4: g_main_context_iteration (gmain.c:3869)
==21491== by 0x846EE55: g_application_run (gapplication.c:2311)
==21491== by 0x44CA4B: main (main.c:57)
https://bugzilla.gnome.org/show_bug.cgi?id=756762
This avoids these warnings:
configure.ac:32: warning: AC_PROG_CC was called before AX_CHECK_ENABLE_DEBUG
aclocal.m4:316: AX_CHECK_ENABLE_DEBUG is expanded from...
aclocal.m4:390: GNOME_DEBUG_CHECK is expanded from...
https://bugzilla.gnome.org/show_bug.cgi?id=756762
On panel construction, we trigger asynchronous creation of a GDBusProxy
for the IIO sensors daemon and one for the Screen g-s-d interface.
Since there's no guarantee we'll have the screen proxy ready by the time
the IIO proxy is constructed, guard for (priv->screen_proxy != NULL), or
we'll hit a critical.
https://bugzilla.gnome.org/show_bug.cgi?id=754735
