fix up im_vips2dz args
fix up im_vips2dz args

oops arg processing wasn't right

leiyangyou/libvips,mcanthony/libvips,mcanthony/libvips,mcanthony/libvips,wishabi/libvips,lovell/libvips,wishabi/libvips,leiyangyou/libvips,leiyangyou/libvips,wishabi/libvips,leiyangyou/libvips,jcupitt/libvips,lovell/libvips,lovell/libvips,wishabi/libvips,jcupitt/libvips,mcanthony/libvips,jcupitt/libvips,jcupitt/libvips,lovell/libvips