fix thumbnail badge size
fix thumbnail badge size

the old version gave

  TypeError: cannot concatenate 'str' and 'int' objects

when only one of thumbnail height and width was set on the
instance level.

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