When adding Custom locations and forward hostname doesn't exist than nginx unable to start

[robinkufner-rs]

Checklist

• Have you pulled and found the error with jc21/nginx-proxy-manager:latest docker image?
  • Yes
• Are you sure you're not using someone else's docker image?
  • Yes
• Have you searched for similar issues (both open and closed)?
  • Yes

Describe the bug

Added custom location /database with working host name. Than shut down the host and restarted proxy manager. Proxy manager will no longer start

❯ Starting nginx ...
nginx: [emerg] host not found in upstream "adminer-1" in /data/nginx/proxy_host/3.conf:68

Nginx Proxy Manager Version
2.12.3

To Reproduce
Steps to reproduce the behavior:

1. Go to Custom locations
2. Add new custom location
3. Save
4. Shut down custom location
5. Restart proxy manager
6. See error described above

Proxy manager should be able to ignore the failing configuration and show a warning in the admin ui but still run.