Apply constant-time comparison to the fallback password checks as well.

Change-Id: I8d2aa6448c95266a45b2862f12f1a5d8259f4f0b
Releases: master
Resolves: #79888
Related: #79795
Reviewed-on: https://review.typo3.org/51853


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>