Don't show a addresspicker for cancelled elections

[GeoWill]

When there's a split postcode (between polling districts) and a cancelled election we show an address picker. This isn't necessary so it would be nice to go straight to telling the user about the cancelled elections. This isn't actually that simple, as at the moment we don't distinguish between postcodes split across ballots, vs those split across polling districts.
This specific issue is a nice way of clarifying the more general issue.