NuPlayer: fix behavior of setPlaybackParams.

setPlaybackParams with zero speed is equivalent to pause().
setPlaybackParams with non-zero speed should start playback when player has
been prepared.
Bug: 29032949

Change-Id: Ib7738da653208f4fe5a8f1d7cf98b8479b3dc798
diff --git a/media/libmediaplayerservice/nuplayer/NuPlayer.h b/media/libmediaplayerservice/nuplayer/NuPlayer.h
index 7431532..ae17c76 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayer.h
+++ b/media/libmediaplayerservice/nuplayer/NuPlayer.h
@@ -198,6 +198,7 @@
     AVSyncSettings mSyncSettings;
     float mVideoFpsHint;
     bool mStarted;
+    bool mPrepared;
     bool mResetting;
     bool mSourceStarted;