libmediaplayerservice:Fix deadlock on gapless start failure

Return error back to the application if start of next MediaPlayer
instance as part of gapless transition fails.
Test: compiles
authored-by: Ashish Jain <ashishj@codeaurora.org>
Change-Id: I77c570074c7c98c996122e275161ba88298e56fc
(cherry picked from commit 9eadf496fa84603cf3ec5889990b79db8e378400)
(cherry picked from commit 6cb33759)