Music: Froce close while tapping next button

In MediaPlayer.setNext, it will release current player.
If "MediaPlayer reaching end of file" and "Users tapping
next button" run at the same time, setNext will be invoked twice
in different threads, makes the next player to be release.

Check whether current player will set itself as next.

Change-Id: I7eb376897fb91433f912e18ba6462c69e56b3893
CRs-Fixed: 1114429
1 file changed