bug#7537: 23.2.90; infinite loop in scrolling

[Chong Yidong]

Leo <sdl.web@gmail.com> writes:

> An unstoppable infinite loop can be reproduced by
>
> 1. emacs -Q
> 2. Evaluate the following expression in *scratch* with C-x C-e.
>    (progn
>      (setq scroll-conservatively 100)
>      (setq scroll-preserve-screen-position 'always)
>      (goto-char (point-min))
>      (set-window-vscroll nil 1 t))
>
> Tested in Emacs build with X11 on OSX.
>
> See: http://lists.gnu.org/archive/html/emacs-devel/2010-12/msg00073.html

I've checked in a fix.  Thanks for the bug report.