Fix font preload crash

third_party/WebKit/Source/core/loader/DocumentLoader.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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.
@@ skipping 155 matching lines @@
         break;
     case Resource::Script:
         resource = ScriptResource::fetch(request, fetcher());
         break;
     case Resource::CSSStyleSheet:
         resource = CSSStyleSheetResource::fetch(request, fetcher());
         break;
     case Resource::Font:
         resource = FontResource::fetch(request, fetcher());
         // This is needed for fonts as loading doesn't start until there's usage.
-        toFontResource(resource)->beginLoadIfNeeded(fetcher());
+        if (resource)
+            toFontResource(resource)->beginLoadIfNeeded(fetcher());
         break;
     case Resource::Media:
         resource = RawResource::fetchMedia(request, fetcher());
         break;
     case Resource::TextTrack:
         resource = RawResource::fetchTextTrack(request, fetcher());
         break;
     case Resource::ImportResource:
         resource = RawResource::fetchImport(request, fetcher());
         break;
@@ skipping 581 matching lines @@
 {
     m_writer = createWriterFor(ownerDocument, init, mimeType(), m_writer ? m_writer->encoding() : emptyAtom, true, ForceSynchronousParsing);
     if (!source.isNull())
         m_writer->appendReplacingData(source);
     endWriting(m_writer.get());
 }
 
 DEFINE_WEAK_IDENTIFIER_MAP(DocumentLoader);
 
 } // namespace blink