* lisp/image/image-converter.el (image-convert-p): Update
image-converter-regexp when image-converter was customized (bug#39994).
;; Find an installed image converter.
(unless image-converter
(image-converter--find-converter))
+ ;; When image-converter was customized
+ (if (and image-converter (not image-converter-regexp))
+ (when-let ((formats (image-converter--probe image-converter)))
+ (setq image-converter-regexp (concat "\\." (regexp-opt formats) "\\'"))))
(and image-converter
(or (and (not data-p)
(string-match image-converter-regexp source))