f - take channel_state lock only when needed

Author: ViktorTigerstrom

lightning/src/ln/channelmanager.rs

@@ -2241,14 +2241,14 @@ impl<Signer: Sign, M: Deref, T: Deref, K: Deref, F: Deref, L: Deref> ChannelMana
 			}
 		};
 
-		let mut channel_state = self.channel_state.lock().unwrap();
 		if let &PendingHTLCStatus::Forward(PendingHTLCInfo { ref routing, ref amt_to_forward, ref outgoing_cltv_value, .. }) = &pending_forward_info {
 			// If short_channel_id is 0 here, we'll reject the HTLC as there cannot be a channel
 			// with a short_channel_id of 0. This is important as various things later assume
 			// short_channel_id is non-0 in any ::Forward.
 			if let &PendingHTLCRouting::Forward { ref short_channel_id, .. } = routing {
-				let id_option = channel_state.short_to_chan_info.get(&short_channel_id).cloned();
 				if let Some((err, code, chan_update)) = loop {
+					let mut channel_state = self.channel_state.lock().unwrap();
+					let id_option = channel_state.short_to_chan_info.get(&short_channel_id).cloned();
 					let forwarding_id_opt = match id_option {
 						None => { // unknown_next_peer
 							// Note that this is likely a timing oracle for detecting whether an scid is a