Typing a correct but non-existent endpoint is not being handled that well yet

Just tested with an UDP Server endpoint in BlueOS and it worked perfectly :)

I'm going to approve it today so we can merge it for the next Beta.

I had a small problem when inputing a non-existent endpoint, but it didn't gave extra problems in the application nor anything. We should handle those cases better, but it should not hold this PR as it only happens when using the new UDP/TCP endpoints and does not affect anything else. I will open an issue and we can work on that in a following PR. Screenshot attached below.

_Originally posted by @rafaellehmkuhl in https://github.com/bluerobotics/cockpit/issues/2084#issuecomment-3257979851_

Start by reproducing the problem described for a correctly formatted but non-existent UDP or TCP endpoint in BlueOS, using the attached screenshot as context. Trace how the endpoint input is handled and define done as handling the invalid endpoint clearly without causing additional application problems.

Written by the indexing model from the issue text.