Fix files with wrong extension saving as invalid images (fix #806)
Fix files with wrong extension saving as invalid images (fix #806)

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