Merge revision 603 changes:

- Fix memory leak when returning zero-length strings from V8 (issue #581).

git-svn-id: https://chromiumembedded.googlecode.com/svn/branches/963@605 5089003a-bbd8-11dd-ad1f-f1f9622dbc98

include/internal/cef_string_wrappers.h

@@ -411,7 +411,7 @@ public:
   ///
   void clear()
   {
-    if (!empty())
+    if (string_)
       traits::clear(string_);
   }