notmuch.el: Avoid warning about referencing free variable `button'.

I'm not even sure how the previous code worked at all---it seems
clear it was supposed to be using `cite-button' rather than `button'.

diff --git a/notmuch.el b/notmuch.el
index 28ef5c6b4e8af4729db502a83a2fa0ddb717737e..94a6384419ad1a46cb744e6820f603c56c1b2ef1 100644 (file)
--- a/notmuch.el
+++ b/notmuch.el
@@ -545,7 +545,7 @@ which this thread was originally shown."
   (goto-char (button-start (previous-button (point)))))
 
 (defun notmuch-toggle-invisible-action (cite-button)
-  (let ((invis-spec (button-get button 'invisibility-spec)))
+  (let ((invis-spec (button-get cite-button 'invisibility-spec)))
         (if (invisible-p invis-spec)
             (remove-from-invisibility-spec invis-spec)
           (add-to-invisibility-spec invis-spec)