[BUGFIX] Guard array key access in `SetupModuleController`

Prevent an undefined array key warning in case
a non-admin-user save his profile with disabled
avatar field, for example with

  setup.fields.avatar.disabled=1

Resolves: #103873
Releases: main, 12.4
Change-Id: I1c91fb65b8508445928a5ec405b9447f452c1fdc
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84339


Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>