Fixes a deadlock occurring with certain DirectShow filters when stopping a streamed video (see QTBUG-8420 for test code and video).
Fixes a deadlock occurring with certain DirectShow filters when stopping a streamed video (see QTBUG-8420 for test code and video).

shadeslayer/phonon-gstreamer,KDE/phonon-directshow,KDE/phonon-xine,KDE/phonon-xine,KDE/phonon-directshow,KDE/phonon-gstreamer,KDE/phonon-xine,KDE/phonon-mmf,KDE/phonon-gstreamer,shadeslayer/phonon-gstreamer,KDE/phonon-waveout,KDE/phonon-quicktime,shadeslayer/phonon-gstreamer