Prevent generating an error during ws close (#4127)

When a WebSocket connection was closing it was sending a message after
it was closed already. This generated an error in the logs.
While this error didn't harm any of the functionallity of Vaultwarden it
isn't nice to see them of course.

This PR Fixes this by catching the close message and breaks the loop at
that point. This prevents the `_` catch-all from replying the close
message back to the client, which was causing the error message.

Fixes #4090