Added a wrapString(const char*) which automatically handles null strings.

include/osgDB/Output

@@ -49,6 +49,9 @@ class OSGDB_EXPORT Output : public std::ofstream
 
         Output& indent();
 
+        /** wrap a string with "" quotes and use \" for any internal quotes.*/
+        std::string wrapString(const char* str);
+
         /** wrap a string with "" quotes and use \" for any internal quotes.*/
         std::string wrapString(const std::string& str);