TYPO3 Core

For the UID of the `headerThumbnail`, the first array entry in the configured field is used.

But when debugging the record (`$rec` / `$data['databaseRow']`), we see, it is just the raw record, which means a FAL-field will not be an array but only an integer that counts the relations...
This way, `$fileUid`will always stay empty.

\TYPO3\CMS\Backend\Form\Container\InlineRecordContainer:

$fieldValue = $rec[$inlineConfig['appearance']['headerThumbnail']['field']];
$fileUid = $fieldValue[0]['uid'];