[BUGFIX] FILES.folder does not work

cObject IMAGE was executed with empty values
because given key contains filenames instead of
numbers

Resolves: #45724
Releases: 6.2, 6.1, 6.0
Change-Id: I5582b63080b7e6124c3780a8430efb410876a662
Reviewed-on: https://review.typo3.org/25016
Reviewed-by: Gernot Ploiner
Tested-by: Gernot Ploiner
Reviewed-by: Wouter Wolters
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind

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

@@ -138,7 +138,7 @@ class FilesContentObject extends \TYPO3\CMS\Frontend\ContentObject\AbstractConte
 					try {
 						$folder = $this->getFileFactory()->getFolderObjectFromCombinedIdentifier($folderIdentifier);
 						if ($folder instanceof \TYPO3\CMS\Core\Resource\Folder) {
-							$this->addToArray($folder->getFiles(), $fileObjects);
+							$this->addToArray(array_values($folder->getFiles()), $fileObjects);
 						}
 					} catch (\TYPO3\CMS\Core\Resource\Exception $e) {
 						/** @var \TYPO3\CMS\Core\Log\Logger $logger */