[BUGFIX] Fix undefined array key warnings in field providers

Resolves: #95995
Releases: master
Change-Id: I6faea581aba0ca9171a6b79c94c1371c56b60387
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72192


Tested-by: Nikita Hovratov <nikita.h@live.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>