(XXX: TESTME) Move pending payment tracking to after the new HTLC flies

If we attempt to send a payment, but the HTLC cannot be send due to
local channel limits, we'll provide the user an error but end up
with an entry in our pending payment map. This will result in the
user not being able to retry their payment as we'll consider it
still "in-flight".

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -1960,7 +1960,6 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 			starting_block_height: self.best_block.read().unwrap().height(),
 			total_msat: total_value,
 		});
-		assert!(payment.insert(session_priv_bytes, path.last().unwrap().fee_msat));
 
 		let err: Result<(), _> = loop {
 			let mut channel_lock = self.channel_state.lock().unwrap();
@@ -1978,12 +1977,17 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 					if !chan.get().is_live() {
 						return Err(APIError::ChannelUnavailable{err: "Peer for first hop currently disconnected/pending monitor update!".to_owned()});
 					}
-					break_chan_entry!(self, chan.get_mut().send_htlc_and_commit(htlc_msat, payment_hash.clone(), htlc_cltv, HTLCSource::OutboundRoute {
-						path: path.clone(),
-						session_priv: session_priv.clone(),
-						first_hop_htlc_msat: htlc_msat,
-						payment_id,
-					}, onion_packet, &self.logger), channel_state, chan)
+					let send_res =
+						break_chan_entry!(self, chan.get_mut().send_htlc_and_commit(
+							htlc_msat, payment_hash.clone(), htlc_cltv, HTLCSource::OutboundRoute {
+								path: path.clone(),
+								session_priv: session_priv.clone(),
+								first_hop_htlc_msat: htlc_msat,
+								payment_id,
+							}, onion_packet, &self.logger),
+						channel_state, chan);
+					assert!(payment.insert(session_priv_bytes, path.last().unwrap().fee_msat));
+					send_res
 				} {
 					Some((update_add, commitment_signed, monitor_update)) => {
 						if let Err(e) = self.chain_monitor.update_channel(chan.get().get_funding_txo().unwrap(), monitor_update) {