Fix crash in QMediaPlaylist.
Fix crash in QMediaPlaylist.

A non-null playlist control does not guarantee a non-null mediaObject.

enthought/qt-mobility,qtproject/qt-mobility,enthought/qt-mobility,kaltsi/qt-mobility,enthought/qt-mobility,enthought/qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,KDE/android-qt-mobility,qtproject/qt-mobility,enthought/qt-mobility,qtproject/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,qtproject/qt-mobility,kaltsi/qt-mobility,KDE/android-qt-mobility,tmcguire/qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,KDE/android-qt-mobility,KDE/android-qt-mobility,kaltsi/qt-mobility,tmcguire/qt-mobility,enthought/qt-mobility,qtproject/qt-mobility