[BUGFIX] prevent exception on filelist module

Author: Achim Fritz

Classes/Backend/EventListener/ModifyButtonBarEventListener.php

@@ -36,6 +36,9 @@ public function __invoke(ModifyButtonBarEvent $event): void
         $request = $this->getRequest();
         $pageId = $request->getQueryParams()['id'] ?? 0;
         $page = $this->pageRepository->getPage($pageId);
+        if (empty($page)) {
+            return;
+        }
 
         if ((int)($page['doktype'] ?? 0) === (int)(EmailTemplateService::getTypoScript()['doktype'] ?? 0)) {
             $plaintextTypeNum = (int)(EmailTemplateService::getTypoScript()['typeNum'] ?? 0);