[BUGFIX] Omit exception using localized file metadata with RTE

Translating extended sys_file_metadata with an RTE field throwed an
exception because the iso code of a language id > 0 cannot be determined.
A null value was returned which violates the method's return type. As
a solution, English is returned.

Resolves: #92248
Releases: master, 10.4
Change-Id: I47ff6e3452ab7e31c1d9cd9e58a00d62fbffae0d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/65654


Tested-by: Oliver Hader <oliver.hader@typo3.org>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>