Fix https://github.com/chrislusf/seaweedfs/issues/825#issuecomment-469097375

weed/server/master_grpc_server.go

@@ -102,12 +102,13 @@ func (ms *MasterServer) SendHeartbeat(stream master_pb.Seaweed_SendHeartbeatServ
 
 		// tell the volume servers about the leader
 		newLeader, err := t.Leader()
-		if err == nil {
-			if err := stream.Send(&master_pb.HeartbeatResponse{
-				Leader: newLeader,
-			}); err != nil {
-				return err
-			}
+		if err != nil {
+			return err
+		}
+		if err := stream.Send(&master_pb.HeartbeatResponse{
+			Leader: newLeader,
+		}); err != nil {
+			return err
 		}
 	}
 }