Fix a playback bug for mediaplayer windows media foundation backend

Task-number:QTMOBILITY-1606

Reviewed-by:Jonas Rabbe
(cherry picked from commit d5426bf52e19c9c6a52837b423f48024979ea076)

Change-Id: Ie7c1c90a8f5a64e77c435ffc1917d8f9638dfff3
Reviewed-on: http://codereview.qt-project.org/5499
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

src/plugins/wmf/player/mfplayersession.h

@@ -94,7 +94,7 @@ public:
     }
 
     void load(const QMediaContent &media, QIODevice *stream);
-    void stop();
+    void stop(bool immediate = false);
     void start();
     void pause();