[BUGFIX] Avoid undefined array key "enableMetaphoneSearch"

Resolves: #100883
Releases: main, 12.4, 11.5
Change-Id: I89f566a1bdf45f214a175cd389ef143c6334cda3
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79056
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>

typo3/sysext/indexed_search/Classes/Controller/AdministrationController.php

@@ -148,7 +148,7 @@ public function initializeAction()
     {
         $this->pageUid = (int)($this->request->getQueryParams()['id'] ?? 0);
         $this->indexerConfig = GeneralUtility::makeInstance(ExtensionConfiguration::class)->get('indexed_search');
-        $this->enableMetaphoneSearch = (bool)$this->indexerConfig['enableMetaphoneSearch'];
+        $this->enableMetaphoneSearch = (bool)($this->indexerConfig['enableMetaphoneSearch'] ?? false);
 
         parent::initializeAction();
     }