Investigate GLib-GObject-CRITICAL warnings

[Jigoku]

Since introduction of bookmarks manager, these warnings/critical messages have been appearing again. They don't appear to be making the application misbehave, so it's been hard to find where they are coming from.

Noting here as a reminder.

(alluvion-gtk.pl:2018): GLib-GObject-CRITICAL **: g_object_get_qdata: assertion 'G_IS_OBJECT (object)' failed

(alluvion-gtk.pl:2018): GLib-GObject-CRITICAL **: g_object_steal_qdata: assertion 'G_IS_OBJECT (object)' failed

(alluvion-gtk.pl:2018): GLib-GObject-CRITICAL **: g_object_unref: assertion 'G_IS_OBJECT (object)' failed

(alluvion-gtk.pl:2018): GLib-GObject-CRITICAL **: g_signal_handlers_destroy: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed

(alluvion-gtk.pl:2018): GLib-GObject-CRITICAL **: g_object_unref: assertion 'G_IS_OBJECT (object)' failed
Gtk-CRITICAL **: IA__gtk_widget_get_realized: assertion 'GTK_IS_WIDGET (widget)' failed during global destruction.
GLib-GObject-WARNING **: instance with invalid (NULL) class pointer during global destruction.

(alluvion-gtk.pl:2018): GLib-GObject-CRITICAL **: g_signal_emit_valist: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed
GLib-GObject-WARNING **: instance with invalid (NULL) class pointer during global destruction.

(alluvion-gtk.pl:2018): GLib-GObject-CRITICAL **: g_signal_handlers_destroy: assertion 'G_TYPE_CHECK_INSTANCE (instance)' failed
GLib-GObject-WARNING **: instance with invalid (NULL) class pointer during global destruction.

[Jigoku]

On the 3rd search result, it appears to trigger the warnings.

[Jigoku]

Exists in 0.2 also.
0.1 doesn't share this behavior, i have a strong feeling it is to do with populating the bookmarks tab.

Each action after the first errors, introduces more and more errors, after time it builds up and bogs down the application causing a segfault too.

[Jigoku]

Then again, i just disabled on_window_check_resize on a whim, and the errors disappeared completely... all thread finish cleanly, and the application does not segfault (it appears).

This seems to be the problem... opening new issue.
#34