[BUGFIX] Prevent redirection loop for shortcuts

This patch prevents the redirection to another page if the returned
URL is empty which would trigger a redirection loop.

Releases: master, 6.2
Resolves: #65447
Change-Id: Ida0fc65c83d32ca7ae45db2d02b87d7eb0c8d345
Reviewed-on: http://review.typo3.org/37446


Reviewed-by: Frank Nägler <typo3@naegler.net>
Tested-by: Frank Nägler <typo3@naegler.net>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>