bug#17761: 24.3.91; smie-for-sexp and parentheses of-by-one bug?

[Leo Liu <sdl.web@gmail.com>]

1. Open a buffer in octave mode and insert ( ) with point between the
   parentheses

2. Eval (smie-forward-sexp) which should give back something like
   (t 2 ")")

POS is before the token ")" instead of the end position of the token. Is
this a bug? This can often cause infinite loop if one is not careful.

BTW, although smie-config-guess's return value is not documented, it
seems no harm to do something like the following:

=== modified file 'lisp/emacs-lisp/smie.el'
--- lisp/emacs-lisp/smie.el	2014-03-04 08:35:11 +0000
+++ lisp/emacs-lisp/smie.el	2014-06-12 11:20:38 +0000
@@ -2156,7 +2156,7 @@
       (user-error "This buffer does not seem to be using SMIE"))
   (let ((config (smie-config--guess (point-min) (point-max))))
     (cond
-     ((null config) (message "Nothing to change"))
+     ((null config) (message "Nothing to change") nil)
      ((null smie-config--buffer-local)
       (message "Local rules set")
       (setq smie-config--buffer-local config))

Thanks,
Leo