Fix division by 0 problem in calculation of Glass object size
Fix division by 0 problem in calculation of Glass object size

- if there are no images to show in GroupSelector, width of glass box
  is set to default values`

NguyenMatthieu/f-spot,mono/f-spot,mono/f-spot,dkoeb/f-spot,mans0954/f-spot,mono/f-spot,dkoeb/f-spot,mans0954/f-spot,mans0954/f-spot,NguyenMatthieu/f-spot,dkoeb/f-spot,mono/f-spot,mans0954/f-spot,mono/f-spot,NguyenMatthieu/f-spot,dkoeb/f-spot,mono/f-spot,NguyenMatthieu/f-spot,mans0954/f-spot,mans0954/f-spot,dkoeb/f-spot,dkoeb/f-spot,NguyenMatthieu/f-spot