fix may be used uninitialized warning on older compilers

Source/core/rendering/FastTextAutosizer.h

 /*
  * Copyright (C) 2013 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 59 matching lines @@
         explicit LayoutScope(Document& document, RenderBlock* block)
         {
             m_textAutosizer = document.fastTextAutosizer();
             if (m_textAutosizer) {
                 if (!m_textAutosizer->enabled()) {
                     m_textAutosizer = 0;
                     return;
                 }
                 m_block = block;
                 m_textAutosizer->beginLayout(m_block);
+            } else {
+                m_block = 0;
             }
         }
 
         ~LayoutScope()
         {
             if (m_textAutosizer)
                 m_textAutosizer->endLayout(m_block);
         }
     private:
         FastTextAutosizer* m_textAutosizer;
@@ skipping 122 matching lines @@
     // cluster root. Clusters whose roots share the same fingerprint use the
     // same multiplier.
     SuperclusterMap m_superclusters;
     ClusterStack m_clusterStack;
     FingerprintMapper m_fingerprintMapper;
 };
 
 } // namespace WebCore
 
 #endif // FastTextAutosizer_h