ox-koma-letter: Fix void `with-title' variable

* contrib/lisp/ox-koma-letter.el (org-koma-letter-template): Let-bind
  `with-title'.

Reported-by: Thomas Holst <Thomas_Holst@gmx.de>
<http://permalink.gmane.org/gmane.emacs.orgmode/98349>

contrib/lisp/ox-koma-letter.el

@@ -617,11 +617,12 @@ holding export options."
    (format "\\date{%s}\n" (org-export-data (org-export-get-date info) info))
    ;; Hyperref, document start, and subject and title.
    (let* ((with-subject (plist-get info :with-subject))
+	  (with-title (plist-get info :with-title))
 	  (title-as-subject (and with-subject
 				 (plist-get info :with-title-as-subject)))
 	  (subject* (org-string-nw-p
 		     (org-export-data (plist-get info :subject) info)))
-	  (title* (and (plist-get info :with-title)
+	  (title* (and with-title
 		       (org-string-nw-p
 			(org-export-data (plist-get info :title) info))))
 	  (subject (cond ((not with-subject) nil)