invoices: store custom records in invoice database

invoices/invoiceregistry_test.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/htlcswitch/hop"
 	"github.com/lightningnetwork/lnd/lntypes"
 	"github.com/lightningnetwork/lnd/lnwire"
 	"github.com/lightningnetwork/lnd/record"
@@ -669,3 +670,7 @@ type mockPayload struct {
 func (p *mockPayload) MultiPath() *record.MPP {
 	return p.mpp
 }
+
+func (p *mockPayload) CustomRecords() hop.CustomRecordSet {
+	return make(hop.CustomRecordSet)
+}