[BUGFIX] Make BackendUtility::viewOnClick honor doc

Make parameter $alternativeUrl work as documented in the docblock
and also as it worked until #22157.
This patch preserves the hook and basically just puts in an
if-statement. Also adding a unit test.

Change-Id: I7d67af438b0a0af51ca7662b3f8286aeec827c77
Fixes: #41165
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/22620
Reviewed-by: Markus Klein
Tested-by: Markus Klein