[BUGFIX] Fix PHP 8 warning in ImageResourceContentObject

Added null coalescing operator in case $lastImgResourceInfo[3]
is not set.

Resolves: #99004
Releases: main, 11.5
Change-Id: Ieca6d193db884917785705b2468fcfe3ced623e2
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78003


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>

typo3/sysext/frontend/Classes/ContentObject/ImageResourceContentObject.php

@@ -36,7 +36,7 @@ class ImageResourceContentObject extends AbstractContentObject
         if (!is_array($lastImgResourceInfo)) {
             return '';
         }
-        $imageResource = $lastImgResourceInfo[3];
+        $imageResource = $lastImgResourceInfo[3] ?? '';
         return isset($conf['stdWrap.']) ? $this->cObj->stdWrap($imageResource, $conf['stdWrap.']) : $imageResource;
     }
 }