another call_user_func warning fix

inc/parser/renderer.php

@@ -75,7 +75,7 @@ class Doku_Renderer extends DokuWiki_Plugin {
       foreach ( $instructions as $instruction ) {
         // execute the callback against ourself
         if (method_exists($this,$instruction[0])) {
-          call_user_func_array(array($this, $instruction[0]),$instruction[1]);
+          call_user_func_array(array($this, $instruction[0]), $instruction[1] ? $instruction[1] : array());
         }
       }
     }