[BUGFIX] Fix clipboard thumbnail rendering

The thumbnail rendering in filelist clibboard isn't
updated to use FAL. And adding folders to clipboard
with thumbnails enabled results in a fatal error.

This changes makes sure the thumbnail is only rendered
for files and updates the thumbnail part so it uses FAL.

Resolves: #56037
Releases: 6.2, 6.1
Change-Id: I2a0eccd633f5313fed9ab94b5081c13e08892900
Reviewed-on: https://review.typo3.org/27653
Tested-by: Wouter Wolters
Reviewed-by: Wouter Wolters
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring