[TASK] Don't render table header if no files given

It doesn't make sense to render the table header in
the filelist module if no files are given.

Change-Id: I81870bca94e63643e3f27c90efa370b0a9964337
Resolves: #45579
Releases: 6.1
Reviewed-on: https://review.typo3.org/18362
Reviewed-by: Felix Kopp
Tested-by: Felix Kopp
Reviewed-by: Soren Malling
Tested-by: Soren Malling
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn