[pvr] fix built-in PlayMedia with PVR channels and recordings (Trac #15164)

This should fixes the playback of PVR channels and recordings with the built-in PlayMedia as reported at http://trac.kodi.tv/ticket/15164
This is why I suggested that `CPVRManager` handles getting a `CFileItem` instance and `CApplication` is the one that actually calls `PlayMedia`, now we have to duplicate the last line instead. I still think we could just return false here, since if an item `IsPVR` but not actually a channel or a recording, what is it and why should we even try to play it?