WMF: release video controls before releasing the session

For the VideoRendererControl, also stop the video surface at the same
time.
This fixes a crash when changing video.

Change-Id: I49484f8b277c345dafb3e5947cf5d23df15546f3
Reviewed-by: Jason Barron <jason@cutehacks.com>

src/plugins/wmf/player/mfvideorenderercontrol.h

@@ -59,6 +59,7 @@ public:
     void setSurface(QAbstractVideoSurface *surface);
 
     IMFActivate* createActivate();
+    void releaseActivate();
 
 protected:
     void customEvent(QEvent *event);