bugfix getColumnNames (stwe#886)

Author: stephanvierkant

Twig/DatatableTwigExtension.php

@@ -182,7 +182,7 @@ public function datatablesRenderFilter(Twig_Environment $twig, DatatableInterfac
         $searchColumn = $this->accessor->getValue($filter, 'searchColumn');
 
         if (null !== $searchColumn) {
-            $columns = $datatable->getColumnNames();
+            $columns = $datatable->getColumnBuilder()->getColumnNames();
             $searchColumnIndex = $columns[$searchColumn];
         } else {
             $searchColumnIndex = $index;