[BUGFIX] Make sure that foreach loops are applied to arrays only

Fix some foreach loops so as not to run into potentially empty elements.
Use the ?? operator to accomplish that.

Change-Id: Id6306cea0546dfd4a20ba98c170335966cc2ae40
Resolves: #83322
Releases: master, 8.7
Reviewed-on: https://review.typo3.org/55066


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>