[TASK] Avoid PHP Notice in RedirectService

Resolves: #90112
Releases: master
Change-Id: Iddccd7525992428142e7daff6c44a206f20e435b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/62888


Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Guido Schmechel <guido.schmechel@brandung.de>
Tested-by: Tobi Kretschmann <tobi@tobishome.de>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Felix P. <f.pachowsky@neusta.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Guido Schmechel <guido.schmechel@brandung.de>
Reviewed-by: Tobi Kretschmann <tobi@tobishome.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>

typo3/sysext/redirects/Classes/Service/RedirectService.php

@@ -212,7 +212,7 @@ class RedirectService implements LoggerAwareInterface
         }
         // Do this for files, folders, external URLs
         if (!empty($linkDetails['url'])) {
-            if ($matchedRedirect['is_regexp']) {
+            if ($matchedRedirect['is_regexp'] ?? false) {
                 $linkDetails = $this->replaceRegExpCaptureGroup($matchedRedirect, $uri, $linkDetails);
             }