[RFC] unicode: Completion of error handling

[Markus Elfring]

Hello,

It can be determined (also with the help of some source code analysis tools)
that error detection (and corresponding exception handling) is incomplete
in this source file.
https://elixir.bootlin.com/linux/v6.18-rc4/source/fs/unicode/mkutf8data.c
https://cwe.mitre.org/data/definitions/252.html

How do you think about to improve affected implementation details?

Regards,
Markus