[BUGFIX] Database integrity check fatal error

If a file or directory below uploads/ is not readable by the
executing user, the integrity check system in db check module
menu may fatal. This is sanatized by the patch.

Resolves: #51460
Releases: 6.2, 6.1, 6.0
Change-Id: Ide3401c014aa7bec33585083f81f30c00100da09
Reviewed-on: https://review.typo3.org/23424
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn
(cherry picked from commit 81d22419488af753e394d82fc1338feff0c5795c)
Reviewed-on: https://review.typo3.org/23467