fix panic in router metrics

chain/route.go

@@ -119,10 +119,12 @@ func (r *Route) connect(ctx context.Context) (conn net.Conn, err error) {
 	}
 	node.Marker.Reset()
 
+	if r.chain != nil {
 		if v := metrics.GetObserver(metrics.MetricNodeConnectDurationObserver,
 			metrics.Labels{"chain": r.chain.name, "node": node.Name}); v != nil {
 			v.Observe(time.Since(start).Seconds())
 		}
+	}
 
 	preNode := node
 	for _, node := range r.nodes[1:] {