[BUGFIX] Avoid undefined array key "pointer." in AbstractPlugin

Resolves: #99106
Releases: main, 11.5
Change-Id: Iabddf0b2f1c98db6e3e07f26162257f696d6fd9f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76616


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>