bus: Unreferencing messages outside the lock
bus: Unreferencing messages outside the lock

Shouldn't take the lock while unreferencing messages, because that may cause
more messages to be sent, which will try to take the lock and cause the app to
hang.

Fixes https://bugzilla.gnome.org/show_bug.cgi?id=728777

StreamUtils/gstreamer,jpxiong/gstreamer,shelsonjava/gstreamer,centricular/gstreamer,StreamUtils/gstreamer,shelsonjava/gstreamer,jpxiong/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,mparis/gstreamer,krichter722/gstreamer,centricular/gstreamer,jpxiong/gstreamer,centricular/gstreamer,mparis/gstreamer,centricular/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer,jpxiong/gstreamer,StreamUtils/gstreamer,krichter722/gstreamer,shelsonjava/gstreamer,krichter722/gstreamer,StreamUtils/gstreamer,jpxiong/gstreamer,centricular/gstreamer,mparis/gstreamer,mparis/gstreamer,mparis/gstreamer,StreamUtils/gstreamer