[BUGFIX] Handle disabled default language in PageContentErrorHandler

The SiteInterface provides the "getDefaultLanguage()"
method, which will always return the first configured
language - usually L=0. However, this language might
be disabled, which means, it should not be visible
in frontend context.

The PageContentErrorHandler therefore now tries
to fetch the first enabled language, in case the
requested language id does not exist in the current
site and the sites' default language is disabled.

Resolves: #99530
Releases: main, 11.5
Change-Id: Ib02cbd8f01a4fc1a69be46ad2015e8863553fae0
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/77440


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