[BUGFIX] concatenateJs/Css does not consider forceOnTop

Setting the forceOnTop property for a JS or CSS file is not
observed if concatenateJs/Css is set as well.

Resolves: #53116
Resolves: #56019
Releases: 6.2, 6.1
Change-Id: Ica31656bd72f4a0249513206bac45aa16b929761
Reviewed-on: https://review.typo3.org/27640
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters