The issue happens when the structure is printed by the logging
subsystem: the object is included in the log, and this will cause the
full object printout to be done there. However, after dispose, the queue
was already cleared, so the access to it (to print the object) would
assert, as the queue was already freed. The patch changes it so that the
queue is merely empty, and only freed in _finalize.

https://bugzilla.gnome.org/show_bug.cgi?id=776293