[BUGFIX] Allow relative URLs in locationHeaderUrl

Resolves: #81720
Releases: master, 8.7
Change-Id: I099c905bf335a13fafa920c2849fd88971dc0e44
Reviewed-on: https://review.typo3.org/58705


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Joerg Kummer <typo3@enobe.de>
Tested-by: Joerg Kummer <typo3@enobe.de>
Reviewed-by: Ursula Klinger <klinger@punkt.de>
Tested-by: Ursula Klinger <klinger@punkt.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>