Remove unreachable error case in construct_fwd_pending_htlc_info

Since we completed handling for all wrong-payload-provided cases in the
previous commit, we can remove an unreachable error on constructing pending
HTLC info. This simplifies error handling down the line since we won't need
even more unreachable code for handling a construct_fwd_pending_htlc_info intro
node error.

lightning/src/ln/channelmanager.rs

@@ -2719,7 +2719,7 @@ where
 		&self, msg: &msgs::UpdateAddHTLC, hop_data: msgs::InboundOnionPayload, hop_hmac: [u8; 32],
 		new_packet_bytes: [u8; onion_utils::ONION_DATA_LEN], shared_secret: [u8; 32],
 		next_packet_pubkey_opt: Option<Result<PublicKey, secp256k1::Error>>
-	) -> Result<PendingHTLCInfo, InboundOnionErr> {
+	) -> PendingHTLCInfo {
 		debug_assert!(next_packet_pubkey_opt.is_some());
 		let outgoing_packet = msgs::OnionPacket {
 			version: 0,
@@ -2731,16 +2731,16 @@ where
 		let (short_channel_id, amt_to_forward, outgoing_cltv_value) = match hop_data {
 			msgs::InboundOnionPayload::Forward { short_channel_id, amt_to_forward, outgoing_cltv_value } =>
 				(short_channel_id, amt_to_forward, outgoing_cltv_value),
-			msgs::InboundOnionPayload::Receive { .. } =>
-				return Err(InboundOnionErr {
-					msg: "Final Node OnionHopData provided for us as an intermediary node",
-					err_code: 0x4000 | 22,
-					err_data: Vec::new(),
-				}),
-			_ => todo!()
+			msgs::InboundOnionPayload::Receive { .. } |
+				msgs::InboundOnionPayload::BlindedReceive { .. } |
+				msgs::InboundOnionPayload::BlindedForward { .. } =>
+			{
+				// We checked for this case in [`Self::decode_update_add_htlc_onion`].
+				unreachable!()
+			}
 		};
 
-		Ok(PendingHTLCInfo {
+		PendingHTLCInfo {
 			routing: PendingHTLCRouting::Forward {
 				onion_packet: outgoing_packet,
 				short_channel_id,
@@ -2751,7 +2751,7 @@ where
 			outgoing_amt_msat: amt_to_forward,
 			outgoing_cltv_value,
 			skimmed_fee_msat: None,
-		})
+		}
 	}
 
 	fn construct_recv_pending_htlc_info(
@@ -3152,11 +3152,10 @@ where
 				}
 			},
 			onion_utils::Hop::Forward { next_hop_data, next_hop_hmac, new_packet_bytes } => {
-				match self.construct_fwd_pending_htlc_info(msg, next_hop_data, next_hop_hmac,
-					new_packet_bytes, shared_secret, next_packet_pubkey_opt) {
-					Ok(info) => PendingHTLCStatus::Forward(info),
-					Err(InboundOnionErr { err_code, err_data, msg }) => return_err!(msg, err_code, &err_data)
-				}
+				let fwd_info = self.construct_fwd_pending_htlc_info(
+					msg, next_hop_data, next_hop_hmac, new_packet_bytes, shared_secret, next_packet_pubkey_opt
+				);
+				PendingHTLCStatus::Forward(fwd_info)
 			}
 		}
 	}