[BUGFIX] Absolute URIs get prefixed with absRefPrefix in typolink

An absolute URI (e.g. "/folder/someFile.png") gets prefixed with
absRefPrefix (e.g. "/") which results in "//folder/someFile.png",
which is a schema-less URI notation and thus "folder" is
interpreted as hostname.

Resolves: #72846
Releases: master, 7.6
Change-Id: Ic49c0a24a17f754c6c89186e6041b9857eb967b1
Reviewed-on: https://review.typo3.org/46113


Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>