[BUGFIX] Fix linktype selection in Linkvalidator report

* handle uninitialized values
* do not show all results in report if no linktypes checked

Resolves: #84010
Releases: master, 8.7
Change-Id: Id04d2eed1b1390f2cbf67fd971d7cc4d61539f15
Reviewed-on: https://review.typo3.org/55872


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: Frank Naegler <frank.naegler@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>