Should check whether document.settings() is available or not when updating GenericFontFamilySetting…

Source/core/css/CSSFontSelector.cpp

 /*
  * Copyright (C) 2007, 2008, 2011 Apple Inc. All rights reserved.
  *           (C) 2007, 2008 Nikolas Zimmermann <zimmermann@kde.org>
  *
  * 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
@@ skipping 141 matching lines @@
 #if !ENABLE(OILPAN)
 void CSSFontSelector::clearDocument()
 {
     m_fontLoader->clearResourceFetcher();
     m_document = nullptr;
 }
 #endif
 
 void CSSFontSelector::updateGenericFontFamilySettings(Document& document)
 {
-    ASSERT(document.settings());
+    if (!document.settings())
+        return;
     m_genericFontFamilySettings = document.settings()->genericFontFamilySettings();
 }
 
 void CSSFontSelector::trace(Visitor* visitor)
 {
     visitor->trace(m_document);
     visitor->trace(m_fontFaceCache);
     visitor->trace(m_clients);
     visitor->trace(m_fontLoader);
     FontSelector::trace(visitor);
 }
 
 }