[BUGFIX] Prevent undefined array key errors in TcaSelectItems

This adjust `TcaSelectItems` to prevent some
undefined array key errors.

Resolves: #105706
Releases: main, 13.4, 12.4
Change-Id: I1dd8ddfb8bac3643b772ebc7e20c522cbdf2514f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/87254
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: Oliver Bartsch <bo@cedev.de>

Author: o-ba

typo3/sysext/backend/Classes/Form/FormDataProvider/TcaSelectItems.php

@@ -151,7 +151,7 @@ public function addInvalidItemsFromDatabase(array $result, $table, $fieldName, a
     {
         // Early return if there are no items or invalid values should not be displayed
         if (empty($fieldConf['config']['items'])
-            || $fieldConf['config']['renderType'] !== 'selectSingle'
+            || ($fieldConf['config']['renderType'] ?? '') !== 'selectSingle'
             || ($result['pageTsConfig']['TCEFORM.'][$table . '.'][$fieldName . '.']['disableNoMatchingValueElement'] ?? false)
             || ($fieldConf['config']['disableNoMatchingValueElement'] ?? false)
         ) {
@@ -201,6 +201,6 @@ public function addInvalidItemsFromDatabase(array $result, $table, $fieldName, a
      */
     protected function isTargetRenderType(array $fieldConfig)
     {
-        return $fieldConfig['config']['renderType'] !== 'selectTree';
+        return ($fieldConfig['config']['renderType'] ?? '') !== 'selectTree';
     }
 }