GenericSource: reset mPrepareBuffering to initial value when buffering monitor is stopped.

Bug: 26676177
Change-Id: I4dbd86a624bd0c8fb8dd154752e345168e804d6b
diff --git a/media/libmediaplayerservice/nuplayer/GenericSource.cpp b/media/libmediaplayerservice/nuplayer/GenericSource.cpp
index f4dbdeb..669cfe4 100644
--- a/media/libmediaplayerservice/nuplayer/GenericSource.cpp
+++ b/media/libmediaplayerservice/nuplayer/GenericSource.cpp
@@ -1572,7 +1572,7 @@
     mIsStreaming = isStreaming;
     mAudioTimeUs = 0;
     mVideoTimeUs = 0;
-    mPrepareBuffering = true;
+    mPrepareBuffering = (cachedSource != NULL || wvmExtractor != NULL);
     cancelPollBuffering_l();
     mOffloadAudio = false;
     mFirstDequeuedBufferRealUs = -1ll;