[BUGFIX] Avoid PHP undefined array access in BrowseLinksController

Resolves: #103360
Releases: main, 12.4
Change-Id: I6331f4ed9d061a06962d0e70affa43bc239a78a9
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83401
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Reviewed-by: Jasmina Ließmann <minapokhalo+typo3@gmail.com>

typo3/sysext/rte_ckeditor/Classes/Controller/BrowseLinksController.php

@@ -99,8 +99,8 @@ protected function initVariables(ServerRequestInterface $request): void
         $queryParameters = $request->getQueryParams();
         $this->siteUrl = $request->getAttribute('normalizedParams')->getSiteUrl();
         $this->currentLinkParts = $queryParameters['P']['curUrl'] ?? [];
-        $this->editorId = $queryParameters['editorId'];
-        $this->contentsLanguage = $queryParameters['contentsLanguage'];
+        $this->editorId = $queryParameters['editorId'] ?? '';
+        $this->contentsLanguage = $queryParameters['contentsLanguage'] ?? '';
         $this->contentLanguageService = $this->languageServiceFactory->create($this->contentsLanguage);
         $tcaFieldConf = [
             'enableRichtext' => true,