MediaPlayerService: clear output in CallbackData when recycling AudioTrack.

Bug: 30365636
Change-Id: I3832a309f78a6fa89d4afea7bdd7139f0d9013f4
diff --git a/media/libmediaplayerservice/MediaPlayerService.cpp b/media/libmediaplayerservice/MediaPlayerService.cpp
index d790821..3cfed5e 100644
--- a/media/libmediaplayerservice/MediaPlayerService.cpp
+++ b/media/libmediaplayerservice/MediaPlayerService.cpp
@@ -1938,6 +1938,7 @@
                     continue;
                 }
                 callbackData->mSwitching = true; // begin track switch
+                callbackData->setOutput(NULL);
 #else
                 // tryBeginTrackSwitch() returns false if the callback has the lock.
                 if (!mCallbackData->tryBeginTrackSwitch()) {