org-contacts.el: Only use org-id-store-link if org-id is loaded

Fixes bug introduced in 6b83c6e4e that made org-contacts-anniversaries
error if org-id was not loaded.

contrib/lisp/org-contacts.el

@@ -1166,7 +1166,7 @@ are effectively trimmed).  If nil, all zero-length substrings are retained."
   "Store the contact in `org-contacts-files' with a link."
   (when (and (eq major-mode 'org-mode)
 	     (member (buffer-file-name) (mapcar 'expand-file-name org-contacts-files)))
-    (if org-id-link-to-org-use-id
+    (if (and (featurep 'org-id) org-id-link-to-org-use-id)
 	(org-id-store-link)
       (let ((headline-str (substring-no-properties (org-get-heading t t t t))))
 	(org-store-link-props