Fix link fontification

* lisp/org.el (org-activate-links): Display description when
  available.

Reported-by: Marco Wahl <marcowahlsoft@gmail.com>
<http://lists.gnu.org/r/emacs-orgmode/2019-03/msg00117.html>

lisp/org.el

@@ -5325,8 +5325,8 @@ This includes angle, plain, and bracket links."
 			       ,(or (org-link-get-parameter type :display)
 				    'org-link))
 			     properties))
-		    (visible-start (or (match-beginning 4) (match-beginning 2)))
-		    (visible-end (or (match-end 4) (match-end 2))))
+		    (visible-start (or (match-beginning 3) (match-beginning 2)))
+		    (visible-end (or (match-end 3) (match-end 2))))
 		(add-text-properties start visible-start hidden)
 		(add-text-properties visible-start visible-end properties)
 		(add-text-properties visible-end end hidden)