Only sign funding transaction on monitor update resumption

The `handle_channel_resumption` path is reachable from both channel
reestablish and monitor update completion. Since we only want to sign
once we know the monitor update has completed, it's possible we could
have unintentionally attempted to sign if we were still pending the
monitor update but had a channel reestablish occur.

Author: wpaulino

lightning/src/ln/channelmanager.rs

@@ -9006,10 +9006,13 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 			}
 		}
 
-		if let Some(signing_session) = &mut channel.interactive_tx_signing_session {
-			if signing_session.local_inputs_count() > 0
-				&& signing_session.holder_tx_signatures().is_none()
-			{
+		if let Some(signing_session) = (!channel.is_awaiting_monitor_update())
+			.then(|| ())
+			.and_then(|_| channel.interactive_tx_signing_session.as_mut())
+			.filter(|signing_session| signing_session.holder_tx_signatures().is_none())
+		{
+			let local_inputs_count = signing_session.local_inputs_count();
+			if local_inputs_count > 0 {
 				let mut pending_events = self.pending_events.lock().unwrap();
 				let unsigned_transaction = signing_session.unsigned_tx().build_unsigned_tx();
 				let event_action = (
@@ -9027,7 +9030,8 @@ This indicates a bug inside LDK. Please report this error at https://github.com/
 				} else {
 					pending_events.push_back(event_action);
 				}
-			} else if signing_session.local_inputs_count() == 0 && signing_session.holder_tx_signatures().is_none() {
+			} else {
+				let txid = signing_session.unsigned_tx().compute_txid();
 				match channel.funding_transaction_signed(vec![]) {
 					Ok((Some(tx_signatures), funding_tx_opt)) => {
 						if let Some(funding_tx) = funding_tx_opt {