[BUGFIX] Ensure items array in DataHandler checkValue methods

It is possible that TCA items array is not set in DataHandler if

1. items is defined through types/*/columnsOverrides
2. DataHandler is triggered with context of another record type
   (e.g. by a translation request)

This patch ensures we are always dealing with an array for items. Also,
when passing it as parameter to
`ItemProcessingService->getProcessingItems`.

Resolves: #103472
Releases: main, 12.4
Change-Id: I364841982b7c2913e339bf5a504d811b3e050049
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/83575


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>