share: i18n: fix mismatch in BIG5 esdb generation

In the first loop, we setup Big5_$i_variable where $i are elements of
$PART with : replaced to @. Do the same in the second loop when we're
trying to refer to the same variable.

No functional change, because none of the in-tree mappings have an @
in them.

Sponsored by: Klara, Inc.