Fix null recordsFiltered on empty collection

Fix #2793

Author: yajra

src/DataTableAbstract.php

@@ -869,7 +869,7 @@ protected function render(array $data): JsonResponse
         $output = $this->attachAppends([
             'draw' => $this->request->draw(),
             'recordsTotal' => $this->totalRecords,
-            'recordsFiltered' => $this->filteredRecords,
+            'recordsFiltered' => $this->filteredRecords ?? 0,
             'data' => $data,
         ]);