manual network proxy settings shouldn't allow save when empty

[Alan Pope 🍺🐧🐱 🦄]

Open system settings
Navigate to 'Network'
Click Network-Proxy
Choose 'Manual'
Close the dialog without filling in any proxy details.

It allowed me to save with no warning. With this setting it results in bug 942312 (and perhaps others).

I believe it should prompt, forcing me to fill something in the fields.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-control-center 1:3.3.90-0ubuntu4
Uname: Linux 3.3.0-030300rc1-generic x86_64
ApportVersion: 1.93-0ubuntu2
Architecture: amd64
Date: Wed Feb 29 22:54:32 2012
EcryptfsInUse: Yes
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha amd64 (20120203)
ProcEnviron:
 LANGUAGE=en_GB:en
 TERM=xterm
 PATH=(custom, user)
 LANG=en_GB.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-control-center
UpgradeStatus: No upgrade log present (probably fresh install)
usr_lib_gnome-control-center:
 activity-log-manager-control-center 0.9.2-0ubuntu2
 deja-dup 21.90-0ubuntu1
 gnome-bluetooth 3.2.2-0ubuntu2
 indicator-datetime 0.3.90-0ubuntu1