[BUGFIX] Fix array access warning in SystemStatusUpdateTask

When this task is executed on CLI (scheduler), the global request variable
is not available, thus a null check must be added before checking the instance
of the value.

Releases: 10.4, 11.5, main
Resolves: #99464
Change-Id: Ie9c1b8e4fbc187d6ade569b1b152ce799a09a1f0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77260


Reviewed-by: Torben Hansen <derhansen@gmail.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Helmut Hummel <typo3@helhum.io>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: Torben Hansen <derhansen@gmail.com>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Helmut Hummel <typo3@helhum.io>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Benjamin Kott <benjamin.kott@outlook.com>