[PM] ensure_can_not_dispute_the_same_outcome only checks for the last outcome, but should for each of them

[Chralt98]

While implementing the global disputes mechanism I realised, that each new dispute only compares with the last dispute for a match, but it should compare with all disputes, if there is a match (so that a new dispute gets rejected).

zeitgeist/zrml/prediction-markets/src/lib.rs

Lines 1491 to 1502 in ba6efa8

	fn ensure_can_not_dispute_the_same_outcome(
	disputes: &[MarketDispute<T::AccountId, T::BlockNumber>],
	report: &Report<T::AccountId, T::BlockNumber>,
	outcome: &OutcomeReport,
	) -> DispatchResult {
	if let Some(last_dispute) = disputes.last() {
	ensure!(&last_dispute.outcome != outcome, Error::<T>::CannotDisputeSameOutcome);
	} else {
	ensure!(&report.outcome != outcome, Error::<T>::CannotDisputeSameOutcome);
	}
	Ok(())
	}

[maltekliemann]

This is by design. Think about how it used to be in simple-disputes: Someone disputes A, then someone disputes B. Should A be off the table forever now? No, of course not.

Now that simple-disputes is removed, we could have a discussion about changing this, though.

[Chralt98]

I just realised it in the test, yeah you are right, it makes sense as it was.

[Chralt98]

But on the second look for the global dispute mechanism it would make much sense to change that. So that the users don't dispute on the same outcome. I will add that to the Global dispute PR.

[Chralt98]

Fixed by moving the logic to simple disputes #938