Fix: Yandex city.

Yandex results raise `NoMethodError: undefined method '[]' for nil:NilClass` on `.city`. The schema in http://api.yandex.com/maps/doc/geocoder/desc/yandex-maps-geocoder-desc.pdf describes something a bit more relaxed.

I wonder whether `AdministrativeAreaName` and `SubAdministrativeAreaName` can be cities, but the lookup for `New York, NY` doesn't return a city otherwise.