[BUG] 'case' broken for multi-byte characters

As of this commit:

> commit c5bf9702ea110bede687b57c0b5fa3fd0e15829e (HEAD, refs/bisect/bad)
> Author: Herbert Xu <[email protected]>
> Date:   Sun Jun 2 09:28:59 2024 +0800
> 
>     expand: Add multi-byte support to pmatch
> 
>     Add CTLMBCHAR support to pmatch.
> 
>     POSIX equivalence classes and collating symbols are not unsupported.
> 
>     Enable CTLMBCHAR generation in mbtodest.
> 
>     Signed-off-by: Herbert Xu <[email protected]>

...'case' is broken for multi-byte characters. The following test script, when 
saved in UTF-8, outputs 'BUG' instead of 'ok':

case "ρ" in
( "ρ" )	echo ok ;;
( * )	echo BUG; exit 1 ;;
esac

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