ox-html.el (org-html-format-inline-image): Fix missing string in formatting string

* ox-html.el (org-html-format-inline-image): Fix missing string in
formatting string.

Thanks to Richard Stanton for reporting this.

lisp/ox-html.el

@@ -1226,8 +1226,8 @@ When STANDALONE-P is t, wrap the <img.../> into a <div>...</div>."
       (let ((img (format "<img src=\"%s\" %s/>" src attr)))
 	(format "\n<div%s class=\"figure\">%s%s\n</div>"
 		id (format "\n<p>%s</p>" img)
-		(when (and caption (not (string= caption "")))
-		  (format "\n<p>%s</p>" caption)))))
+		(if (and caption (not (string= caption "")))
+		    (format "\n<p>%s</p>" caption) ""))))
      (t (format "<img src=\"%s\" %s/>" src (concat attr id))))))
 
 (defun org-html--textarea-block (element)