po: msgstr entries with unmatched %-format string

Yutaka Niibe at 2017-12-19T02:34:16Z

The problem of GnuPG key generation only for Japanese was reported: https://dev.gnupg.org/T3619

It is due to unmatched %-format in msgstr (in po/ja.po).

This kind of bug can cause DoS targetted to a specific locale. I think that msgfmt -c should check this, too.