skip deltaBeat if dn is zero (#3630)

* skip deltaBeat
https://github.com/seaweedfs/seaweedfs/issues/3629

* fix GrpcPort

* skip url :0

* skip empty DataCenter or Rack

* skip empty heartbeat Ip

* dell msg add DataCenter

* comment todo

* fix

weed/wdclient/masterclient.go

@@ -262,6 +262,10 @@ func (mc *MasterClient) tryConnectToMaster(master pb.ServerAddress) (nextHintedL
 }
 
 func (mc *MasterClient) updateVidMap(resp *master_pb.KeepConnectedResponse) {
+	if resp.VolumeLocation.IsEmptyUrl() {
+		glog.V(0).Infof("updateVidMap ignore short heartbeat: %+v", resp)
+		return
+	}
 	// process new volume location
 	loc := Location{
 		Url:        resp.VolumeLocation.Url,