Check pending funding in send_htlc

If there are any pending splices when an sending an update_add_htlc
message, the HTLC amount must be validated against each pending
FundingScope. Otherwise, it may be invalid once the splice is locked.

Author: jkczyz

lightning/src/ln/channel.rs

@@ -9140,10 +9140,13 @@ impl<SP: Deref> FundedChannel<SP> where
 			return Err((LocalHTLCFailureReason::ChannelNotReady,
 				"Cannot send HTLC until channel is fully established and we haven't started shutting down".to_owned()));
 		}
-		let channel_total_msat = self.funding.get_value_satoshis() * 1000;
-		if amount_msat > channel_total_msat {
-			return Err((LocalHTLCFailureReason::AmountExceedsCapacity,
-				format!("Cannot send amount {}, because it is more than the total value of the channel {}", amount_msat, channel_total_msat)));
+
+		for funding in core::iter::once(&self.funding).chain(self.pending_funding.iter()) {
+			let channel_total_msat = funding.get_value_satoshis() * 1000;
+			if amount_msat > channel_total_msat {
+				return Err((LocalHTLCFailureReason::AmountExceedsCapacity,
+					format!("Cannot send amount {}, because it is more than the total value of the channel {}", amount_msat, channel_total_msat)));
+			}
 		}
 
 		if amount_msat == 0 {