Protect data source access with mutex during disconnect

Bug: 23658148
Change-Id: Ic37cac7b5d166143e0b77e9919b0aaef486e4fdd
diff --git a/media/libmediaplayerservice/nuplayer/GenericSource.h b/media/libmediaplayerservice/nuplayer/GenericSource.h
index dc85d2d..ac980ef 100644
--- a/media/libmediaplayerservice/nuplayer/GenericSource.h
+++ b/media/libmediaplayerservice/nuplayer/GenericSource.h
@@ -153,6 +153,7 @@
     int32_t mPrevBufferPercentage;
 
     mutable Mutex mReadBufferLock;
+    mutable Mutex mDisconnectLock;
 
     sp<ALooper> mLooper;