Avoid a short_to_chan_info read lock in claim_funds_from_hop

In 453ed11 we started tracking the
counterparty's `node_id` in `HTLCPreviousHopData`, however we were
still trying to look it up using `prev_short_channel_id` in
`claim_funds_from_hop`.

Because we now usually have the counterparty's `node_id` directly
accessible, we should skip the `prev_short_channel_id` lookup.

This will also be more important in the next commit where we need
to look up state for our counterparty to generate
`ChannelMonitorUpdate`s whether we have a live channel or not.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -6839,10 +6839,12 @@ where
 		{
 			let per_peer_state = self.per_peer_state.read().unwrap();
 			let chan_id = prev_hop.channel_id;
-			let counterparty_node_id_opt = match self.short_to_chan_info.read().unwrap().get(&prev_hop.short_channel_id) {
-				Some((cp_id, _dup_chan_id)) => Some(cp_id.clone()),
-				None => None
-			};
+			let counterparty_node_id_opt = prev_hop.counterparty_node_id.or_else(|| {
+				match self.short_to_chan_info.read().unwrap().get(&prev_hop.short_channel_id) {
+					Some((cp_id, _dup_chan_id)) => Some(cp_id.clone()),
+					None => None
+				}
+			});
 
 			let peer_state_opt = counterparty_node_id_opt.as_ref().map(
 				|counterparty_node_id| per_peer_state.get(counterparty_node_id)