[BUGFIX] Check array key existence in TSFE

Resolves: #101452
Releases: main, 12.4, 11.5
Change-Id: Idf803dff6b4941380dbdde30f53548d31b6df575
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/80141
Tested-by: Stefan B�rk <stefan@buerk.tech>
Reviewed-by: Stefan B�rk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>

typo3/sysext/frontend/Classes/Controller/TypoScriptFrontendController.php

@@ -2274,7 +2274,7 @@ protected function processNonCacheableContentPartsAndSubstituteContentMarkers(ar
             // If the split had a comment-end after 32 characters it's probably a split-string
             if (substr($contentPart, 32, 3) === '-->') {
                 $nonCacheableKey = 'INT_SCRIPT.' . substr($contentPart, 0, 32);
-                if (is_array($nonCacheableData[$nonCacheableKey])) {
+                if (is_array($nonCacheableData[$nonCacheableKey] ?? false)) {
                     $label = 'Include ' . $nonCacheableData[$nonCacheableKey]['type'];
                     $timeTracker->push($label);
                     $nonCacheableContent = '';