Always send Shutdown resposnes to Shutdown messages

We always require that any changes to Channel state be committed
immediately (within the same lock) so we should never have
uncommitted changes which would prevent us from sending a Shutdown
response.

Author: TheBlueMatt

src/ln/channel.rs

@@ -2405,11 +2405,9 @@ impl Channel {
 				_ => true
 			}
 		});
-		for htlc in self.pending_outbound_htlcs.iter() {
-			if let OutboundHTLCState::LocalAnnounced(_) = htlc.state {
-				return Ok((None, None, dropped_outbound_htlcs));
-			}
-		}
+		// If we have any LocalAnnounced updates we'll probably just get back a update_fail_htlc
+		// immediately after the commitment dance, but we can send a Shutdown cause we won't send
+		// any further commitment updates after we set LocalShutdownSent.
 
 		let our_shutdown = if (self.channel_state & ChannelState::LocalShutdownSent as u32) == ChannelState::LocalShutdownSent as u32 {
 			None