Dummy doc should be the same type as the original

Compatibility with different renderers, e.g. qc plugin uses an array

syntax.php

@@ -98,7 +98,7 @@ class syntax_plugin_ifauthex extends DokuWiki_Syntax_Plugin
  if(!$shouldRender) {
  // point the renderer's doc to something else, remembering the old one
  $renderer->meta['ifauthex.originalDoc'] = &$renderer->doc;
- $ignoredDoc = '';
+ $ignoredDoc = is_array($renderer->doc) ? [] : '';
  $renderer->doc = &$ignoredDoc;
 
  // do the same for the toc list