Prevent crash on failed hop index out of range

payment.go

@@ -45,6 +45,12 @@ func (r *regolancer) pay(ctx context.Context, invoice *lnrpc.AddInvoiceResponse,
 		return err
 	}
 	if result.Status == lnrpc.HTLCAttempt_FAILED {
+		if result.Failure.FailureSourceIndex >= uint32(len(route.Hops)) {
+			log.Printf(errColorF("%s (unexpected hop index %d, should be less than %d)", result.Failure.Code.String(),
+				result.Failure.FailureSourceIndex), len(route.Hops))
+			return fmt.Errorf("error: %s @ %d", result.Failure.Code.String(),
+				result.Failure.FailureSourceIndex)
+		}
 		nodeCtx, cancel := context.WithTimeout(ctx, time.Minute)
 		defer cancel()
 		node1, err := r.getNodeInfo(nodeCtx, route.Hops[result.Failure.FailureSourceIndex-1].PubKey)