Added missing "const" that was allowing internal pointer to Unicode

string tobe returned as a non-const value


git-svn-id: svn://10.0.0.236/trunk@20676 18797224-902f-48f8-a5cc-f745e15eee43

mozilla/xpcom/string/obsolete/nsString.cpp

@@ -350,7 +350,7 @@ const PRUnichar* nsString::GetUnicode(void) const{
   return mStr;
 }
 
-nsString::operator PRUnichar*() const{
+nsString::operator const PRUnichar*() const{
   return mStr;
 }