Refund notifications for an already void payment through state machine errors

[simonpfry]

Currently the refund process for Sofort is complicated because they don't allow refunds for three days, and until then you can't send a refund request because it'll be denied, so we make a note in the Solidus admin to refund manually.

However when cancelling the order in Solidus it makes the payment void. When the refund is made in Adyen, they still send a notification back which then attempts to process, leading to errors such as:

Cannot transition state via :complete from :void (Reason(s): State cannot transition via "complete")

I guess it should just not try to process such notifications, because the work is already done.