Fix AppRTCDemo crash when room is connected after PC is destroyed.

webrtc/examples/androidapp/src/org/appspot/apprtc/CallActivity.java

 /*
  *  Copyright 2015 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 351 matching lines @@
     // Store existing audio settings and change audio mode to
     // MODE_IN_COMMUNICATION for best possible VoIP performance.
     Log.d(TAG, "Initializing the audio manager...");
     audioManager.init();
   }
 
   // Should be called from UI thread
   private void callConnected() {
     final long delta = System.currentTimeMillis() - callStartedTimeMs;
     Log.i(TAG, "Call connected: delay=" + delta + "ms");
-
+    if (peerConnectionClient == null || isError) {
+      Log.w(TAG, "Call is connected in closed or error state");
+      return;
+    }
     // Update video view.
     updateVideoView();
     // Enable statistics callback.
     peerConnectionClient.enableStatsEvents(true, STAT_CALLBACK_PERIOD);
   }
 
   private void onAudioManagerChangedState() {
     // TODO(henrika): disable video if AppRTCAudioManager.AudioDevice.EARPIECE
     // is active.
   }
@@ skipping 256 matching lines @@
         }
       }
     });
   }
 
   @Override
   public void onPeerConnectionError(final String description) {
     reportError(description);
   }
 }