JAudioTrack: fix uninitialized mFlags

Test: MediaPlayer2Test#testPlaybackRate is not flaky any more
Bug: 112549970
Change-Id: Ieb80acd89bf578bdd683f0344dfe40ffa0d40c08
diff --git a/media/libmediaplayer2/JAudioTrack.cpp b/media/libmediaplayer2/JAudioTrack.cpp
index d42bb1e..3d6879e 100644
--- a/media/libmediaplayer2/JAudioTrack.cpp
+++ b/media/libmediaplayer2/JAudioTrack.cpp
@@ -100,6 +100,7 @@
         jBuilderObj = env->CallObjectMethod(jBuilderObj, jSetSessionId, sessionId);
     }
 
+    mFlags = AUDIO_OUTPUT_FLAG_NONE;
     if (cbf != NULL) {
         jmethodID jSetOffloadedPlayback = env->GetMethodID(jBuilderCls, "setOffloadedPlayback",
                 "(Z)Landroid/media/AudioTrack$Builder;");