fix conversion to OUString in filedlghelper.cxx

in commit c82d9325
"convert remnants of String to OUString in SFX2 module"
when I created the SetToken method, I forgot to make the first
parameter a reference.

Change-Id: Id587e69ff0cdf46f645d8f9d1dc0e110ae80daa5

sfx2/source/dialog/filedlghelper.cxx

@@ -1902,7 +1902,7 @@ void FileDialogHelper_Impl::addGraphicFilter()
 #define GRF_CONFIG_STR      "   "
 #define STD_CONFIG_STR      "1 "
 
-static void SetToken( OUString rOrigStr, sal_Int32 nToken, sal_Unicode cTok, const OUString& rStr)
+static void SetToken( OUString& rOrigStr, sal_Int32 nToken, sal_Unicode cTok, const OUString& rStr)
 {
     const sal_Unicode*  pStr        = rOrigStr.getStr();
     sal_Int32     nLen              = rOrigStr.getLength();