[BUGFIX] FileList uses wrong basefolder for isWithinFolder

Resolves: #65983
Releases: master, 6.2
Change-Id: I3565ff6e7bae2266ff40f610fca8dc7a6f5beb1c
Reviewed-on: http://review.typo3.org/38125


Reviewed-by: Michael Oehlhof <typo3@oehlhof.de>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>