org-checklist.el: Fix dynamically bound variable name.

* org-checklist.el (org-checklist): Fix dynamically bound
variable name.

Thanks to Bernt Hansen for reporting this.

contrib/lisp/org-checklist.el

@@ -129,7 +129,7 @@ of checkbox items"
 			 (a2ps-buffer)))))))))
 
 (defun org-checklist ()
-  (when (member state org-done-keywords)
+  (when (member org-state org-done-keywords) ;; org-state dynamically bound in org.el/org-todo
     (org-make-checklist-export)
     (org-reset-checkbox-state-maybe)))