Inconsistency in representation when non-ISO currency does not have a subunit

[efung]

In currency_iso.yml, for currencies that do not have a subunit, say, the Japanese yen, there is no subunit defined.

However, in currency_non_iso.yml, the XFU and GBX currencies define their subunit as an empty string.

[elfassy]

please open a PR 🙏 Seems to me like a bug with currency_non_iso.yml