[FIX] payment_ogone: fix refunds for 3DS validation
[FIX] payment_ogone: fix refunds for 3DS validation

Complements rev. 9b1009cd5a324b41e90a8d9bc5d412e45b43fc57 to fix the
handling of validation transactions for 3DS-enabled cards.

This handles a few issues:
- make sure to trigger the refund for validation transactions even if
  the first feedback we get is the S2S feedback
- feedback URL called by the users' browser should not reset the payment
  transaction to 'done' when the refund process has been initiated
- status 81 for "refund pending" should not end up with a transaction in
  error. It may be that Ingenico will send a feedback transaction later
  or not at all, but the refund is likely to succeed at that point.

Without this commit, validation transactions would never be refunded for
3DS cards.

Remaining issue: the return_url does not seem to be set for those
validation transactions, so the user ends up on the homepage after
completing the 3DS step.

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