Guard against mLooper == NULL.

Change-Id: I01aa0e47b55d0dffe34525edf9f055a5cb4dc70f
related-to-bug: 8620223
diff --git a/media/libmediaplayerservice/nuplayer/RTSPSource.cpp b/media/libmediaplayerservice/nuplayer/RTSPSource.cpp
index a5ff0ca..50ebf9c 100644
--- a/media/libmediaplayerservice/nuplayer/RTSPSource.cpp
+++ b/media/libmediaplayerservice/nuplayer/RTSPSource.cpp
@@ -66,7 +66,9 @@
 }
 
 NuPlayer::RTSPSource::~RTSPSource() {
-   mLooper->stop();
+    if (mLooper != NULL) {
+        mLooper->stop();
+    }
 }
 
 void NuPlayer::RTSPSource::prepareAsync() {