MediaPlayerService: fix access of mPlayer in client am: 502c2f4053 am: bd7db202c6 am: 03fa67202f am: 263d5a2a70 am: 0844e1a3e8 am: e0f4963584 am: 5cc9f8780c
am: 93ae13644b

Change-Id: I16649e1417e36610e0731da5c47c90a9de169d13