multi: query circuit map inside contractcourt

This commit adds a new config method `QueryIncomingCircuit` that can be
used to query the payment's incoming circuit for giving its outgoing
circuit key.

contractcourt/htlc_success_resolver_test.go

@@ -12,6 +12,7 @@ import (
 	"github.com/davecgh/go-spew/spew"
 	"github.com/lightningnetwork/lnd/chainntnfs"
 	"github.com/lightningnetwork/lnd/channeldb"
+	"github.com/lightningnetwork/lnd/channeldb/models"
 	"github.com/lightningnetwork/lnd/fn"
 	"github.com/lightningnetwork/lnd/input"
 	"github.com/lightningnetwork/lnd/kvdb"
@@ -92,6 +93,11 @@ func newHtlcResolverTestContext(t *testing.T,
 			},
 			HtlcNotifier: htlcNotifier,
 			Budget:       *DefaultBudgetConfig(),
+			QueryIncomingCircuit: func(
+				circuit models.CircuitKey) *models.CircuitKey {
+
+				return nil
+			},
 		},
 		PutResolverReport: func(_ kvdb.RwTx,
 			report *channeldb.ResolverReport) error {