[BUGFIX] Prevent PHP warning using unsetLimit

The extbase implementation "Query" of the
QueryInterface contains a method "unsetLimit".
Calling this method really PHP:unset()'s the
$limit property from Query object. That will
produce various PHP warnings where getLimit()
is called.
As $limit is initialized with null while
instanciation, calling unsetLimit() will now
reset $limit to null again instead of removing
the complete property.

Resolves: #100999
Releases: main, 12.4
Change-Id: I8042823b7b3e8d010787d976c1a469988b618c41
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79423


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>