[BUGFIX] Ensure content object is available in UriBuilder

Since #100623, the content object might be NULL
as it is no longer set up when initializing the
UriBuilder, but instead when handing in the
current PSR-7 request.

This patch adds a fallback for v12 to ensure
having the content object available when
generating frontend urls.

Resolves: #100788
Related: #100623
Releases: main
Change-Id: I733b0019a974889970d63845e3afcff5113570d5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78920


Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Tested-by: Oliver Bartsch <bo@cedev.de>