Test the rest of the workflow for all-STV CVRs.

[vteague]

Parsing works fine for STV CVRs. However, we need to check that all the rest of the workflow also still works.

The STV contests should be entirely dropped, so I can't see any way for that to cause subsequent trouble. However, there is one possible state that STV creates, which otherwise isn't reachable, which is the state in which a county has uploaded a file that doesn't have any contests.

(If you try to do this with a plain blank file it throws an ArrayIndexOutOfBounds exception.)

So there are two parts to this card:

1. Check that all workflows still work if a county has uploaded an all-STV (and hence effectively blank) CSV.
2. Check with CDOS whether this is expected behaviour, or whether it should instead throw an error (like the non-STV case).