[BUGFIX] Prevent PHP warning for invalid page title in PageLinkHandler

In case a stored page link, links to an invalid page (e.g. pid=0)
or a no longer existing page, the corresponding array access
must be omitted. Also the call to GU::fixed_lgd_cs should be
skipped.

Resolves: #97075
Releases: main, 11.5
Change-Id: I2055a2dfcde021efdd1fa8b20804595d7a40eac2
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73775


Tested-by: core-ci <typo3@b13.com>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>