[BUGFIX] Prevent empty categories in NewContentElementWizard

This patch prevents empty categories in the wizard and prevents an
undefined array key warning.

Resolves: #102990
Releases: main, 12.4
Change-Id: Iec69d1d3e3df66d9a054dfe382afe3d282fec332
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82704


Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/82712


Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Oliver Bartsch <bo@cedev.de>