Fixed wrong username error with multiple quassel networks

Fixed wrong username error, caused by wrong string split. section('c',start,end) defaults to end=-1 -> section('c',0) is complete string.

see http://qt-project.org/doc/qt-4.8/qstring.html#section
Merge pull request #1 from netzvieh/multinetworkfix

Fixed wrong username error with multiple quassel networks