BidiResolver should not try to reverse runs when the run count is zero

Source/core/platform/text/BidiRunList.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2006, 2007, 2008 Apple Inc.  All right reserved.
  * Copyright (C) 2011 Google, Inc.  All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 183 matching lines @@
     }
 
     m_firstRun = 0;
     m_lastRun = 0;
     m_runCount = 0;
 }
 
 template <class Run>
 void BidiRunList<Run>::reverseRuns(unsigned start, unsigned end)
 {
+    if (!m_runCount)
+        return;
+
     if (start >= end)
         return;
 
     ASSERT(end < m_runCount);
 
     // Get the item before the start of the runs to reverse and put it in
     // |beforeStart|. |curr| should point to the first run to reverse.
     Run* curr = m_firstRun;
     Run* beforeStart = 0;
     unsigned i = 0;
@@ skipping 30 matching lines @@
         m_firstRun = endRun;
 
     startRun->m_next = afterEnd;
     if (!afterEnd)
         m_lastRun = startRun;
 }
 
 } // namespace WebCore
 
 #endif // BidiRunList