Add more explicit error message in zoom window (fix #715)
Add more explicit error message in zoom window (fix #715)

Bionus/imgbrd-grabber,Bionus/imgbrd-grabber,Bionus/imgbrd-grabber,Bionus/imgbrd-grabber,YoukaiCat/imgbrd-grabber,Bionus/imgbrd-grabber,YoukaiCat/imgbrd-grabber,Bionus/imgbrd-grabber