OutboundPayments::abandon_payment doesn't wait for the payment to fail to generate a PaymentFailed Event

[TheBlueMatt]

See discussion at #2142 (comment)

[alecchendev]

Since this is marked with the upcoming milestone if it's easier for someone else to pick this up feel free to take it from me, otherwise I'll have a PR open tomorrow!

[alecchendev]

I noticed in OutboundPayments::abandon_payment (and in abandon_entry) it only pushes an Event::PaymentFailed if payment.get().remaining_parts() == 0 which from what I understand means there aren't any pending HTLCs. From the other places where Event::PaymentFailed is pushed (fail_htlc and check_retry_payments), it seems like this is mainly what it means for the payment to have failed (given it's either PendingOutboundPayment::Abandoned or exhausted the retry strategy) - would this mean the issue is resolved or is there something I'm missing?

(Btw I realized I mispoke in #2142 (comment) about PaymentFailed being "directly" pushed in abandon_payment)

[TheBlueMatt]

Ah! Yes, this is not a bug, then. Indeed, as long as we check the remaining_parts is 0 before pushing the event we're good. I must've missed it when I was skimming the code before opening this issue. Sorry for the noise.