org-agenda.el (org-agenda-custom-commands): Fix default setting

* org-agenda.el (org-agenda-custom-commands): Fix default
setting so that the customize interface does not complain
about a mismatch.

lisp/org-agenda.el

@@ -383,8 +383,8 @@ This will be spliced into the custom type of
 `org-agenda-custom-commands'.")
 
 
-(defcustom org-agenda-custom-commands '(("n" "Agenda and all TODO's"
-					 ((agenda "") (alltodo))))
+(defcustom org-agenda-custom-commands
+  '(("n" "Agenda and all TODO's" ((agenda "") (alltodo ""))))
   "Custom commands for the agenda.
 These commands will be offered on the splash screen displayed by the
 agenda dispatcher \\[org-agenda].  Each entry is a list like this: