NuPlayer: check mSource before deferencing it.

Bug: 17428608
Change-Id: I7b264d1288ed3c495434aedeeeef2fbfc3ca2f16
diff --git a/media/libmediaplayerservice/nuplayer/NuPlayer.cpp b/media/libmediaplayerservice/nuplayer/NuPlayer.cpp
index 4a5d18a..35cc1ee 100644
--- a/media/libmediaplayerservice/nuplayer/NuPlayer.cpp
+++ b/media/libmediaplayerservice/nuplayer/NuPlayer.cpp
@@ -1242,7 +1242,8 @@
     CHECK(msg->findMessage("reply", &reply));
 
     if ((audio && mFlushingAudio != NONE)
-            || (!audio && mFlushingVideo != NONE)) {
+            || (!audio && mFlushingVideo != NONE)
+            || mSource == NULL) {
         reply->setInt32("err", INFO_DISCONTINUITY);
         reply->post();
         return OK;