[BUGFIX] Reset number of results in QueryResult after offset changes

Using offsetSet or unset allows manipulating the QueryResult manually.
As the result of `count` is cached, offset changes need to reset that
cache to accurately return the correct offset.

Resolves: #76310
Releases: master, 9.5
Change-Id: Ic43f3810766bdb1ee02800b07f6853c81ba404f5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63919


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>