[BUGFIX] Fix Content-Disposition header sent by dumpFileContents

This patch changes the Content-Disposition header so it is also
send when $asDownload isn't set with value inline and the filename
is between quotes.

Resolves: #56923
Releases: 6.2
Change-Id: Ic47c7d3743e7bac73936d20addbc61193e6fd49c
Reviewed-on: https://review.typo3.org/28399
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Stefan Neufeind
Tested-by: Stefan Neufeind