Make blinded hop features optional per spec.

The spec states that if these features are missing, we MUST process the message
as if it were present and contained an empty array.

Author: valentinewallace

lightning/src/blinded_path/payment.rs

@@ -169,7 +169,7 @@ impl Readable for BlindedPaymentTlvs {
 				short_channel_id,
 				payment_relay: payment_relay.ok_or(DecodeError::InvalidValue)?,
 				payment_constraints: payment_constraints.0.unwrap(),
-				features: features.ok_or(DecodeError::InvalidValue)?,
+				features: features.unwrap_or_else(BlindedHopFeatures::empty),
 			}))
 		} else {
 			if payment_relay.is_some() || features.is_some() { return Err(DecodeError::InvalidValue) }

pending_changelog/blinded-hop-features-optional.txt

@@ -0,0 +1,5 @@
+## Bug Fixes
+
+* LDK previously would fail to forward an intermediate blinded payment
+	if the blinded hop features were absent, potentially breaking
+	interoperability.