Fixed crash when QMediaObject is deleted before QMediaRecorder.

Change-Id: I8a1674b6f3d2b2c9ab888facff21f94af41b81de
Reviewed-on: http://codereview.qt.nokia.com/3544
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

tests/auto/qmediarecorder/tst_qmediarecorder.h

@@ -70,6 +70,7 @@ public slots:
 private slots:
     void testNullService();
     void testNullControls();
+    void testDeleteMediaObject();
     void testError();
     void testSink();
     void testRecord();