[BUGFIX] Linkvalidator: Improve tolerance on HEAD-request error

Force second URL-request if first response had an HTTP-status-code
which indicates a client-error (4xx) or a server-error (5xx).

Resolves: #58145
Releases: master, 6.2
Change-Id: I5cb02a6345494ffbe23caba652628b91812aea37
Reviewed-on: http://review.typo3.org/35025
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>