fix AttributeError in repoze.what when a badge has no group
fix AttributeError in repoze.what when a badge has no group

User.groups contained None if one of the badges assigned to an user
is not related to a group. This fixes::

  AttributeError: 'NoneType' object has no attribute 'group_name'

alkadis/vcv,alkadis/vcv,phihag/adhocracy,phihag/adhocracy,SysTheron/adhocracy,DanielNeugebauer/adhocracy,phihag/adhocracy,SysTheron/adhocracy,DanielNeugebauer/adhocracy,liqd/adhocracy,liqd/adhocracy,alkadis/vcv,DanielNeugebauer/adhocracy,SysTheron/adhocracy,alkadis/vcv,DanielNeugebauer/adhocracy,liqd/adhocracy,liqd/adhocracy,phihag/adhocracy,phihag/adhocracy,DanielNeugebauer/adhocracy,alkadis/vcv