[BUGFIX] ext:seo widget: Ensure language exists in site

Ensure the language of the checked record actually exists in
the site, in case orphan records of other languages are
present.

Resolves: #100111
Releases: main
Change-Id: I5cb3d2e09cfc86b5d43eba9e16b3833afe18e6b8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78046


Tested-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Kevin Appelt <kevin.appelt@icloud.com>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Kevin Appelt <kevin.appelt@icloud.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>