transform links before checking if they are internal; fixes #4814

git-svn-id: svn://develop.studip.de/studip/trunk@31780 c5b85792-5220-0410-ad23-ed5b6b8ad999
cleanup isLinkIntern code; re #4814

git-svn-id: svn://develop.studip.de/studip/trunk@31781 c5b85792-5220-0410-ad23-ed5b6b8ad999