Move currency check to OffersMessageHandler

Add and move the check for unsupported currencies from
the parsing code to `handle_message` in `ChannelManager`.
This change ensures that we don't fail when parsing an
`InvoiceRequest` for an Offer with a currency.

Author: slanesuke

lightning/src/ln/channelmanager.rs

@@ -67,7 +67,7 @@ use crate::offers::invoice::{Bolt12Invoice, DEFAULT_RELATIVE_EXPIRY, DerivedSign
 use crate::offers::invoice_error::InvoiceError;
 use crate::offers::invoice_request::{DerivedPayerSigningPubkey, InvoiceRequest, InvoiceRequestBuilder};
 use crate::offers::nonce::Nonce;
-use crate::offers::offer::{Offer, OfferBuilder};
+use crate::offers::offer::{Amount, Offer, OfferBuilder};
 use crate::offers::parse::Bolt12SemanticError;
 use crate::offers::refund::{Refund, RefundBuilder};
 use crate::offers::signer;
@@ -11135,6 +11135,13 @@ where
 					None => return None,
 				};
 
+				if let Some(amount) = invoice_request.amount() {
+					if let Amount::Currency { .. } = amount {
+						let error = Bolt12SemanticError::UnsupportedCurrency;
+						return Some((OffersMessage::InvoiceError(error.into()), responder.respond()));
+					}
+				}
+
 				let nonce = match context {
 					None if invoice_request.metadata().is_some() => None,
 					Some(OffersContext::InvoiceRequest { nonce }) => Some(nonce),