"Load Balancers undefined" shown in Graylog node State column during shutdown and statup

## Expected Behavior

A meaningful status is always shown when looking at nodes on the `Cluster Configuration` page.

## Current Behavior

`Load Balancers undefined` is briefly displayed when a Graylog node is shut down or started.


## Steps to Reproduce (for bugs)

1. Be on `6.2.x` or newer (and presumably have multiple nodes so you can see the state change)
2. Navigate to the `Cluster Configuration` page
3. Restart one of your cluster's nodes
4. Note that during shutdown and startup you'll briefly see `Load Balancers undefined` for the node on the `Cluster Configuration` page

## Context

## Your Environment

* Graylog Version: `6.2.2`