[BUGFIX] If User TSConfig disables avatar it gets lost when saved

If the user is not allow to modify the avatar it gets
lost since there was no distinction between deleted and
not allowed to modify causing the avatar to be deleted
on save.

Resolves: #80002
Releases: master
Change-Id: I1cf6fa93c2af1122c481b52860990c2433d86594
Reviewed-on: https://review.typo3.org/51860


Reviewed-by: Josef Glatz <josef.glatz@typo3.org>
Tested-by: Josef Glatz <josef.glatz@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: TYPO3com <no-reply@typo3.com>