[BUGFIX] Use traverse() in TypoScript conditions (#632)

Removes potential for error messages in PHP 8

Author: mabolek

Configuration/TypoScript/setup.typoscript

@@ -1,5 +1,4 @@
-[backend.user.isLoggedIn && (request.getQueryParams()['frontend_editing'] == true || request.getQueryParams()['route'] matches '#^/ajax/frontend-editing/#')]
-
+[backend.user.isLoggedIn && (traverse(request.getQueryParams(), 'frontend_editing') == true || traverse(request.getQueryParams(), 'route') matches '#^/ajax/frontend-editing/#')]
   lib.fluidContent {
     stdWrap {
       editIcons = tt_content:header