reenable webp shrink-on-load in thumbnail
reenable webp shrink-on-load in thumbnail

the breakage is in animated webp load with preshrink rather than
thumbnail

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