[BUG] SetPages method do nothing

[g-mero]

// SetPages sets the number of pages in the Image
// For animated images this corresponds to the number of frames

func (r *ImageRef) SetPages(pages int) error {
	out, err := vipsCopyImage(r.image)
	if err != nil {
		return err
	}

	vipsSetImageNPages(r.image, pages)

	r.setImage(out)
	return nil
}

I attempted to use the SetPages method to keep only the first frame of an animated image and export it to a JPEG file, but it doesn't work. After reviewing the code, it appears to merely duplicate the original image.

[songjiayang]

How about setting the page=1 in vips.ImportParams, then just load one page for animated images