[BUGFIX] Add support for language -1 to TCA field type slug

Use default language as fallback for records with sys_language_uid = -1

Resolves: #87067
Releases: master, 9.5
Change-Id: If57d5566b83f4bba79451e8595337ca6c0eb3fc9
Reviewed-on: https://review.typo3.org/59029


Tested-by: TYPO3com <noreply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Tested-by: Mona Muzaffar <mona.muzaffar@gmx.de>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>