bug#15437: 24.3.50; mouse-face extends to an extra character when inside overlay after-string

[Eli Zaretskii]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Mon, 23 Sep 2013 04:47:55 +0300
> 
> 
> 1. Evaluate this definition:
> 
> (defun mouse-face-test ()
>   (interactive)
>   (goto-char (point-min))
>   (insert "aaaaaaaa")
>   (let ((o (make-overlay (point-min) (point))))
>     (overlay-put o 'invisible t)
>     (overlay-put o 'after-string
>                  (concat (propertize "bbbb"
>                                      'face 'next-error
>                                      'mouse-face 'highlight)
>                          "aaaa"))))
> 
> 2. Open a new buffer, type `M-x mouse-face-test'.
> 
> 3. Hover the mouse cursor above the "b" letters. When the cursor is
> away, they're highlighted with the `next-error' face, and the "a"
> letters are untouched. But when the mouse hovers, the first of the "a"
> letters is also highlighted, with the `highlight' face. It shouldn't be.

Fixed in trunk revision 114439.