fix disable png info

        existing_pnginfo['parameters'] = geninfo

    if extension.lower() == '.png':

        if opts.enable_pnginfo:

            pnginfo_data = PngImagePlugin.PngInfo()

            for k, v in (existing_pnginfo or {}).items():

                pnginfo_data.add_text(k, str(v))

        else:

            pnginfo_data = None

        image.save(filename, format=image_format, quality=opts.jpeg_quality, pnginfo=pnginfo_data)