* lisp/image/image-dired.el (image-dired-display-thumbs) (image-dired-forward-image, image-dired-slideshow-start) (image-dired-line-up-interactive): Prefer plusp to open-coding it.
* lisp/image/image-dired.el (image-dired-display-thumbs) (image-dired-forward-image, image-dired-slideshow-start) (image-dired-line-up-interactive): Prefer plusp to open-coding it.