Inconsitent whitelist display from whitelist link in notification creation

## Expected Behavior
When setting up a new notification with the type "HTTP Notification" and typing in a URL graylog suggest to add the URL to the whitelist. The link opens a window where the current whitelisted URLs are displayed and a new URL can be entered.

## Current Behavior
The creation of an entry in the whitelist works but when changing the URL in the "New Notification" form opening the whitelist overlay again the display of the other entries are inconsistent. Sometimes you get the whole list with previously saved whitelist entries and sometimes only the new entry.

## Steps to Reproduce (for bugs)
1. Go to Alerts
2. Go to Notifications
3. Go to Get started
4. Set title to test
5. Set Notification Type to HTTP Notification
6. Set URL to http://localhost/
7. Go to "add to URL Whitelist"
8. enter name and save
9. change URL to https://localhost/
10. Go to "add to URL Whitelist"
11. List is empty
12. When overlay is cancelled and reopened the list appears again

## Context
Occured in automated test development

## Your Environment

* Graylog Version: 4.0.7ja
* Java Version: 11.0.11
* Elasticsearch Version:
* MongoDB Version:
* Operating System: ubuntu
* Browser version: FF 92