Don't format tags in title if title headline does not have tags

* org-exp.el (org-export-get-title-from-subtree): Don't format tags in
title if title headline does not have tags.

Fixes a bug reported by John Hendy in
<CA+M2ft_UnBVfUbmoUX6J2MY7e_9w+7an5n23rAarpnnQnaV=ZA@mail.gmail.com>.

lisp/org-exp.el

@@ -2205,7 +2205,7 @@ can work correctly."
 	;; This is a subtree, we take the title from the first heading
 	(goto-char rbeg)
 	(looking-at org-todo-line-tags-regexp)
-	(setq title (if (eq tags t)
+	(setq title (if (and (eq tags t) (match-string 4))
 			(format "%s\t%s" (match-string 3) (match-string 4))
 		      (match-string 3)))
 	(org-unmodified