vips_thumbnail_buffer: add optional open_args argument (#1147)
vips_thumbnail_buffer: add optional open_args argument (#1147)

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