Prevent double disconnects in RTSPSource

Prevent a null pointer from occuring by checking that we are not
already disconnected before performing a disconnect, in case
multiple disconnects have been issued.

Change-Id: Ib88800cd246086fd57f77d10748d41b1aefe2084
diff --git a/media/libmediaplayerservice/nuplayer/RTSPSource.cpp b/media/libmediaplayerservice/nuplayer/RTSPSource.cpp
index cf455bd..f2d5571 100644
--- a/media/libmediaplayerservice/nuplayer/RTSPSource.cpp
+++ b/media/libmediaplayerservice/nuplayer/RTSPSource.cpp
@@ -459,6 +459,10 @@
 }
 
 void NuPlayer::RTSPSource::onDisconnected(const sp<AMessage> &msg) {
+    if (mState == DISCONNECTED) {
+        return;
+    }
+
     status_t err;
     CHECK(msg->findInt32("result", &err));
     CHECK_NE(err, (status_t)OK);