[democracy] illegal votes can be placed even though the proposal should be voted on anymore

[clangenb]

Here, we see that the proposal state is updated after the new tally has been placed:

pallets/democracy/src/lib.rs

Line 294 in 67ffcfb

match Self::do_update_proposal_state(proposal_id) {

.

Wrong Behaviour:

• If the proposal is too old, it gets cancelled, but the tally is still updated even though the vote didn't count anymore. However, the behaviour isn't wrong, except for that the turnout is one more than was counted, actually.
• If the proposal is in confirming: Actual wrong behaviour. We count the vote even though we should first check if it is still passing and then maybe approve the proposal already. So the bug is that a Nay can put the proposal back to OnGoing even though it should have been approved.

Solution:

• I suggest we should simply update the proposal state as a first step and only insert the new tally the proposal is OnGoing or Confirming and then we have to update the proposal state again.