FS#1995, add a little defense to avoid warnings caused by bad wiki

syntax

inc/parser/renderer.php

@@ -74,7 +74,9 @@ class Doku_Renderer extends DokuWiki_Plugin {
 
       foreach ( $instructions as $instruction ) {
         // execute the callback against ourself
-        call_user_func_array(array(&$this, $instruction[0]),$instruction[1]);
+        if (method_exists($this,$instruction[0])) {
+          call_user_func_array(array($this, $instruction[0]),$instruction[1]);
+        }
       }
     }