fix pyZeroconf bug where getServiceInfo returns None.
This allows the discovery window to work with targets using Avahi to advertise their services.
(patch obtained from <http://sourceforge.net/tracker/?func=detail&aid=1600775&group_id=100909&atid=628622>)

[TOPOLOGY]
NetName=None
Nodes=0x02
Node16Present=0x01
Node16Name=DS401_Slave_GUI
Node16DCFName=DS401_Slave_Gui.eds
Node32Present=0x01
Node32Name=GUI2
Node32DCFName=DS401_Slave_Gui.eds
EDSBaseName=eds