Unlike QNetworkProxy, Chromium's net::ProxyServer expects the hostname and port
to be at default values for special schemes (DIRECT and INVALID). Otherwise, a
DCHECK is triggered at proxy_server.cc:73.

Change-Id: I1ac6c425ea03fcbfe084d25c2fd05bf174c753d6
Reviewed-by: Viktor Engelmann <viktor.engelmann@qt.io>