[BUGFIX] Force argument additionalConfig of MediaViewHelper as array

Make a type cast for the argument additionalConfig as it might be that
it is set as null.
Even though the original cause might be in fluid standalone, it is easy to
fix it in the meantime in our code base.

Resolves: #89148
Releases: master, 9.5
Change-Id: If8c8a5addae1fa527a0d2b5fd01a6e6691d9af8b
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63593


Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Christian Eßl <indy.essl@gmail.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Frank Nägler <frank.naegler@typo3.org>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Frank Nägler <frank.naegler@typo3.org>