undefined error 경고문에 따른 return_url변수 초기화

lib/shop.uri.lib.php

@@ -142,6 +142,7 @@ function shop_short_url_clean($string_url, $url, $page_name, $array_page_names){
             $add_param .= $add_param ? '&'.$add_qry : '?'.$add_qry;
         }
 
+        $return_url = '';
         foreach($s as $k => $v) { $return_url .= '/'.$v; }
 
         return $host.$return_url.$add_param.$fragment;