Prevent that all is called twice for DokuWikiNameSpace

Fixes T4

DokuWikiObjectRepresentation.class.php

@@ -216,7 +216,9 @@ class DokuWikiIterator {
     $callback($ns);
     foreach($ns->nodes as $node) {
       /** $node DokuWikiNode */
+      if ($node instanceof DokuWikiPage) {
         $callback($node);
+      }
       if ($node instanceof DokuWikiNameSpace) {
         $this->_all($node,$callback);
       }