Music: Lack of gapless effect

Right now MediaPlayer.setNextMediaPlayer() will be invoked
after prepare(), at this time it may be that OnPreparedListener
message has not dispatch yet due to different thread.

Do setNextMediaPlayer() on OnPreparedListener to make sure
MediaPlayer is prepared.

Change-Id: I3e8cd260a9ad999227c989c07ff5ffaabeffbb08
CRs-Fixed: 1078042
1 file changed