Fix crash when the OfflineAudioContext constructor is given 0 as numberOfFrames

Source/modules/webaudio/AudioContext.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 136 matching lines @@
     , m_isOfflineContext(true)
     , m_activeSourceCount(0)
 {
     constructCommon();
 
     // FIXME: the passed in sampleRate MUST match the hardware sample-rate since HRTFDatabaseLoader is a singleton.
     m_hrtfDatabaseLoader = HRTFDatabaseLoader::createAndLoadAsynchronouslyIfNecessary(sampleRate);
 
     // Create a new destination for offline rendering.
     m_renderTarget = AudioBuffer::create(numberOfChannels, numberOfFrames, sampleRate);
+    ASSERT(m_renderTarget);
     m_destinationNode = OfflineAudioDestinationNode::create(this, m_renderTarget.get());
+    ASSERT(m_destinationNode);
 }
 
 void AudioContext::constructCommon()
 {
     ScriptWrappable::init(this);
     // According to spec AudioContext must die only after page navigate.
     // Lets mark it as ActiveDOMObject with pending activity and unmark it in clear method.
     setPendingActivity(this);
 
     FFTFrame::initialize();
@@ skipping 927 matching lines @@
 }
 
 void AudioContext::decrementActiveSourceCount()
 {
     atomicDecrement(&m_activeSourceCount);
 }
 
 } // namespace WebCore
 
 #endif // ENABLE(WEB_AUDIO)