Plugin needs to check for state PAYMENT_STATE_CANCELED

[theschweitz]

Currently, a user can submit a payment & then cancel it after submitting.
Once they've submitted 1 payment, the current system prevents the user from submitting a second payment.

However, the system still allows the user to select "Retry Payment or choose another payment method."
Once the user does this & chooses another payment method, they are prevented from selecting "Connect wallet and pay" on the second payment attempt.

BUT — on the Pretix backend, the first payment is marked Canceled, and the system stops checking for this payment. The new payment is then marked Pending, and users will then submit a second payment, that we eventually need to refund.

Solutions
The payment plugin should be checking for Canceled orders as well.