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=0x01
Node3Present=0x01
Node3Name=MySlave
Node3DCFName=Slave_2_0.eds
EDSBaseName=eds