Drop pending outbound messages on peer disconnection

This shouldn't be required, but it may help prevent some downstream
race conditions due to clients not sending message events quickly
enough and trying to send stale messages before new
channel_reestablish messages.

Author: TheBlueMatt

src/ln/channelmanager.rs

@@ -2603,6 +2603,25 @@ impl ChannelMessageHandler for ChannelManager {
 					true
 				})
 			}
+			pending_msg_events.retain(|msg| {
+				match msg {
+					events::MessageSendEvent::SendAcceptChannel { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::SendOpenChannel { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::SendFundingCreated { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::SendFundingSigned { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::SendFundingLocked { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::SendAnnouncementSignatures { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::UpdateHTLCs { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::SendRevokeAndACK { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::SendClosingSigned { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::SendShutdown { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::SendChannelReestablish { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::BroadcastChannelAnnouncement { .. } => true,
+					events::MessageSendEvent::BroadcastChannelUpdate { .. } => true,
+					events::MessageSendEvent::HandleError { ref node_id, .. } => node_id != their_node_id,
+					events::MessageSendEvent::PaymentFailureNetworkUpdate { .. } => true,
+				}
+			});
 		}
 		for failure in failed_channels.drain(..) {
 			self.finish_force_close_channel(failure);