org-contacts.el: Fix store link function does not return link.

* contrib/lisp/org-contacts.el (org-contacts-link-store): Fix
org-store-link return incorrect link without link type prefix.

contrib/lisp/org-contacts.el

@@ -1172,7 +1172,11 @@ are effectively trimmed).  If nil, all zero-length substrings are retained."
 	(org-store-link-props
 	 :type "org-contact"
 	 :link headline-str
-	 :description headline-str)))))
+	 :description headline-str)
+        (setq desc headline-str)
+        (setq link (concat "org-contact:" headline-str))
+        (org-add-link-props :link link :description desc)
+        link))))
 
 (defun org-contacts--all-contacts ()
   "Return an alist (name . (file . position)) of all contacts in `org-contacts-files'."