Change reinterpret_cast to dynamic_cast so we know what we get
Change reinterpret_cast to dynamic_cast so we know what we get

This restores behavior to how it was before
2730b16f0985025d46e363ecba9ceed75608a2af with qobject_cast.

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