Additional fixes for 'GLib-CRITICAL: Source ID was not found..' messages

I'm on Gentoo and still run 0.4.6 which continuously spews those notorious "GLib_CRITICAL" warnings. After applying commit 0b79d92001450e7f359212d4273100628f6a1693 I was still getting those messages - less, but repeatably e.g. on ssh logout. After digging through various distributions' bug reports *I think* fields used for g_async_queue_unref() also need to be nulled out during finalization.
Disclaimer: I have nil experience with GTK/Glib, so this might be horribly wrong; so far it seems to work without explosions.