[isf-wifidog] Client gets blank page when trying to login to RADIUS based network

[Mark Dammer]

This bug describes the problem:
http://dev.wifidog.org/ticket/775
I had a look into the code and I think the main problem is that the 
authenticators login function either creates a proper user object or it 
returns "false", what is not an object and makes PHP to throw up the 
blank page. Will see if I can tweak the code....