Avoid (theorethical) NPE.

Source/web/AssociatedURLLoader.cpp

 /*
  * Copyright (C) 2010, 2011, 2012 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 183 matching lines @@
 void AssociatedURLLoader::ClientAdapter::didSendData(unsigned long long bytesSent, unsigned long long totalBytesToBeSent)
 {
     if (!m_client)
         return;
 
     m_client->didSendData(m_loader, bytesSent, totalBytesToBeSent);
 }
 
 void AssociatedURLLoader::ClientAdapter::didReceiveResponse(unsigned long, const ResourceResponse& response)
 {
+    if (!m_client)
+        return;
+
     // Try to use the original ResourceResponse if possible.
     WebURLResponse validatedResponse = WrappedResourceResponse(response);
     HTTPResponseHeaderValidator validator(m_options.crossOriginRequestPolicy == WebURLLoaderOptions::CrossOriginRequestPolicyUseAccessControl);
     if (!m_options.exposeAllResponseHeaders)
         validatedResponse.visitHTTPHeaderFields(&validator);
 
     // If there are blocked headers, copy the response so we can remove them.
     const HTTPHeaderSet& blockedHeaders = validator.blockedHeaders();
     if (!blockedHeaders.isEmpty()) {
         validatedResponse = WebURLResponse(validatedResponse);
@@ skipping 150 matching lines @@
         m_loader->cancel();
 }
 
 void AssociatedURLLoader::setDefersLoading(bool defersLoading)
 {
     if (m_loader)
         m_loader->setDefersLoading(defersLoading);
 }
 
 } // namespace blink