[BUGFIX] Respect all filemounts in file collection

The directory selector in a file collection now displays the folders
of all filemounts of a user. Before only the folders of the first
filemount were displayed.

Resolves: #55414
Releases: 6.2
Change-Id: Ic47f5163e2cfc7c89edcba4119f06620ed0fd56e
Reviewed-on: https://review.typo3.org/27119
Reviewed-by: Wouter Wolters
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Frans Saris
Tested-by: Frans Saris