message: fixed PingBalancer checker panic when servers is empty
diff: @@ -374,8 +374,6 @@ impl PingBalancerContext {
  }
  async fn checker_task(self: Arc<Self>) {
  - assert!(!self.servers.is_empty(), "check PingBalancer without any servers");
  -
  if !self.probing_required() {
  self.checker_task_dummy().await
  } else {
  