ActionController: no benchmark for no renderer

Benchmarks should not be shown when the renderer is no longer available.

library/Icinga/Web/Controller/ActionController.php

@@ -348,9 +348,11 @@ class ActionController extends Zend_Controller_Action
             // Cast preference app.show_benchmark to bool because preferences loaded from a preferences storage are
             // always strings
             if ((bool) $user->getPreferences()->get('app.show_benchmark', false) === true) {
+                if (!$this->_helper->viewRenderer->getNoRender()) {
                     $layout->benchmark = $this->renderBenchmark();
                 }
             }
+        }
 
         if ($req->getParam('format') === 'pdf') {
             $layout->setLayout('pdf');