Include invreq in payment onion when sending async payments

Past commits have set us up to include invoice requests in outbound async
payment onions. Here we actually pull the invoice request from where it's
stored in outbound_payments and pass it into the correct utility for inclusion
in the onion on initial send.

Per <lightning/bolts#1149>, when paying a static
invoice we need to include our original invoice request in the HTLC onion since
the recipient wouldn't have received it previously.

lightning/src/ln/outbound_payment.rs

@@ -952,20 +952,26 @@ impl OutboundPayments {
 			payment_hash, recipient_onion.clone(), keysend_preimage, &route, Some(retry_strategy),
 			payment_params, entropy_source, best_block_height
 		);
-		match self.pending_outbound_payments.lock().unwrap().entry(payment_id) {
-			hash_map::Entry::Occupied(entry) => match entry.get() {
-				PendingOutboundPayment::InvoiceReceived { .. }
-				| PendingOutboundPayment::StaticInvoiceReceived { .. } => {
-					*entry.into_mut() = retryable_payment;
+		let mut invoice_request_opt = None;
+		let mut outbounds = self.pending_outbound_payments.lock().unwrap();
+		match outbounds.entry(payment_id) {
+			hash_map::Entry::Occupied(entry) => match entry.remove() {
+				PendingOutboundPayment::InvoiceReceived { .. } => {
+					outbounds.insert(payment_id, retryable_payment);
+				},
+				PendingOutboundPayment::StaticInvoiceReceived { invoice_request, .. } => {
+					invoice_request_opt = Some(invoice_request);
+					outbounds.insert(payment_id, retryable_payment);
 				},
 				_ => return Err(Bolt12PaymentError::DuplicateInvoice),
 			},
 			hash_map::Entry::Vacant(_) => return Err(Bolt12PaymentError::UnexpectedInvoice),
 		}
+		core::mem::drop(outbounds);
 
 		let result = self.pay_route_internal(
-			&route, payment_hash, &recipient_onion, keysend_preimage, None, payment_id,
-			Some(route_params.final_value_msat), onion_session_privs, node_signer,
+			&route, payment_hash, &recipient_onion, keysend_preimage, invoice_request_opt.as_ref(),
+			payment_id, Some(route_params.final_value_msat), onion_session_privs, node_signer,
 			best_block_height, &send_payment_along_path
 		);
 		log_info!(