[BUGFIX] previewLink generation is broken without domain-record

Using the previewLink on pages within the backend on a branch
without a domain record defined, the link generation fails.

Therefore the opened window calls URL http://index.php?...

Change-Id: Icf3ff7087776fa4130316073446d983dd3be1026
Fixes: #34396
Releases: 4.5, 4.6, 4.7
Reviewed-on: http://review.typo3.org/9281
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader