It seems that custom location port forwarding is being ignored (or is it my fault but I hope not)

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

Here is what I did:

1. Set a proxy Host with following parameters:
   
2. Set a custom location with following parameters:
   
3. Note that the adresse masked in red is always the same.

Here is the behaviour:

1. http://sample.test.relis/sandbox redirects to http://sample.test.relis/ on port 80 instead of 4001
2. If I switch proxy host port to 4001, whatever the port in custom location, it goes to 4001

=> My conclusion is that custom location port forwarding is being ignored and using proxy host port instead.

Nginx Proxy Manager Version
2.11.3

Operating System
Just NPM running in docker image

And many thanks for this amazing and very useful project!

Reproduce the reported custom-location setup with Nginx Proxy Manager 2.11.3 using the latest Docker image. Compare requests to the custom-location port with requests to the proxy host port, then trace how the generated Nginx proxy configuration selects the upstream. Done means the custom location forwards to its configured port instead of the proxy host port.