Previously, at two places (in g_object_real_dispose() and shortly before
finalize()), we would call
g_datalist_id_set_data (&object->qdata, quark_weak_notifies, NULL);
This clears @quark_weak_notifies at once and then invokes all
notifications.
This means, if you were inside a notification and called
g_object_weak_unref() on the object for *another* weak-reference, then
an exception failed:
GLib-GObject-FATAL-CRITICAL: g_object_weak_unref_cb: couldn't find weak ref 0x401320(0x16b9fe0)
Granted, maybe inside a GWeakNotify you shouldn't call anything on
where_the_object_was. However, unregistering things (like calling
g_object_weak_unref() should still reasonably work.
Instead, now remove each weak notification one by one and invoke it.
https://gitlab.gnome.org/GNOME/glib/-/issues/1002
053fdd6872