Voting's helper update_status() should save changed status

[ueco-jb]

Originally posted by @ueco-jb in #60 (comment)

Currently that helper might change status, for example from Open to Rejected, if contract expires.
https://github.com/confio/poe-contracts/blob/main/packages/voting-contract/src/state.rs#L206-L208
We are using that to see most recent status when someone tries to vote.
Problem is, if status is Rejected and we return an Error... Then proposal's status will be back Open, because changes were not saved on returned error.

This will be confusing and we should mitigate that.

[ueco-jb]

Actually I just realized, that this is currently mitigated... because queries uses same update_status() helper as well.
So despite status not being correct in memory, it's correct for end user who does the query.