Can't disable a proxy if it has an invalid configuration

Description of problem

Once an user enables a proxy, in order to disable it, the user have to provide a valid configuration or he/she won't be able to save the changes.

Right now is not possible to clear the host/port fields before disabling a proxy because empty fields are invalid.

How reproducible

Always

Steps to Reproduce:

1. Enable a proxy (http or https), provide a valid host/port and save.
2. Clear the host/port fields and disable the proxy.

Actual results

The Save button is disabled because the configuration provided is not valid, even if the user is trying to disable the proxy.

Expected results

The user should be able to clear the proxy configuration before disabling it.

Additional info

Video of reproduction steps: https://jam.dev/c/59c2dffc-8017-4137-9da5-eed01f7c4b9e