[BUGFIX] Fix PHP Notices in cached ext_localconf.php

Resolves: #82920
Releases: master, 8.7
Change-Id: I7a533f56ec68a119c19aad6c87de9dfc2e59dc6a
Reviewed-on: https://review.typo3.org/54557


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: Morton Jonuschat <m.jonuschat@mojocode.de>
Tested-by: Morton Jonuschat <m.jonuschat@mojocode.de>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: Tymoteusz Motylewski <t.motylewski@gmail.com>