Sets MAXBLOCK based on original image size


I hope someone working with Pillow will be able to fix the problem but here is a pull request for a better(?) workaround which should fix https://github.com/matthewwithanm/django-imagekit/issues/231.
My premiss is that utils.process_image always get called, so I set original_size = img.size and pass that to > img_to_fobj > save_image.
Have I neglected something? Is it a style-wise way to pass that parameter?