MediaPlayerService: allow next player to be NULL am: 2828412787 am: f4e00a7c5a am: 0dd714e408 am: de97dbd662 am: a7549d3dce am: c6fdb3d696 am: 629e78c10f
am: 50b9d889e6

Change-Id: I86b58e0cb64d668021a649627e34a0386dcc619a