prevent /0 in eye for width/height 1
prevent /0 in eye for width/height 1

see https://github.com/libvips/libvips/issues/1236

lovell/libvips,jcupitt/libvips,lovell/libvips,lovell/libvips,jcupitt/libvips,jcupitt/libvips,jcupitt/libvips,lovell/libvips