return a null picture identifier in the lock video callback
return a null picture identifier in the lock video callback

BinChengfei/phonon-vlc,BinChengfei/phonon-vlc,panzi/phonon-vlc,panzi/phonon-vlc,KDE/phonon-vlc,KDE/phonon-vlc,KDE/phonon-vlc,BinChengfei/phonon-vlc