[BUGFIX] Handle that FileLinkHandler:resolveFile() can return null

In the method FileLinkHandler:resolveHandlerData() the call
to FileLinkHandler:resolveFile() handles the FileDoesNotExistException
correctly. But if it returns null this will lead to a type error.
This patch handles the null value properly.

Resolves: #104659
Releases: main, 12.4
Change-Id: Iacf3ef8e72d7c18b4b15758da8780d94a9282a96
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85677


Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>