Check that buffer exists before trying to get its duration.

Source/modules/webaudio/AudioBufferSourceNode.cpp

 /*
  * Copyright (C) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1.  Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 365 matching lines @@
     m_buffer = buffer;
 }
 
 unsigned AudioBufferSourceNode::numberOfChannels()
 {
     return output(0)->numberOfChannels();
 }
 
 void AudioBufferSourceNode::start(double when)
 {
-    startPlaying(false, when, 0, buffer()->duration());
+    startPlaying(false, when, 0, buffer() ? buffer()->duration() : 0);
 }
 
 void AudioBufferSourceNode::start(double when, double grainOffset)
 {
-    startPlaying(true, when, grainOffset, buffer()->duration());
+    startPlaying(true, when, grainOffset, buffer() ? buffer()->duration() : 0);
 }
 
 void AudioBufferSourceNode::start(double when, double grainOffset, double grainDuration)
 {
     startPlaying(true, when, grainOffset, grainDuration);
 }
 
 void AudioBufferSourceNode::startPlaying(bool isGrain, double when, double grainOffset, double grainDuration)
 {
     ASSERT(isMainThread());
@@ skipping 103 matching lines @@
 void AudioBufferSourceNode::finish()
 {
     clearPannerNode();
     ASSERT(!m_pannerNode);
     AudioScheduledSourceNode::finish();
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)