Merge 78168 - 2011-02-09 Ryosuke Niwa <rniwa@webkit.org>...

Source/WebCore/editing/VisibleSelection.cpp

Index: Source/WebCore/editing/VisibleSelection.cpp
===================================================================
--- Source/WebCore/editing/VisibleSelection.cpp	(revision 79263)
+++ Source/WebCore/editing/VisibleSelection.cpp	(working copy)
@@ -173,6 +173,9 @@
         s = s.parentAnchoredEquivalent();
         e = e.parentAnchoredEquivalent();
     }
+    
+    if (s.isNull() || e.isNull())
+        return 0;
 
     // VisibleSelections are supposed to always be valid.  This constructor will ASSERT
     // if a valid range could not be created, which is fine for this callsite.