bug#19553: 25.0.50; vertical-motion returns erroneous positive value

[Eli Zaretskii]

> From: Dmitry Gutov <dgutov@yandex.ru>
> Date: Sat, 10 Jan 2015 09:21:12 +0300
> 
> 1. Create an empty buffer.
> 
> 2. Create an overlay at the end of it with a tricky after-string:
> 
> (setq my-ov (make-overlay (point-max) (point-max) nil t t))
> (overlay-put my-ov 'after-string "~\n~\n~")
> 
> 3. Move point to the end of the buffer (it will be rendered after the
> display string; not sure if it's a bug).
> 
> 4. Evaluate (vertical-motion 1). Point won't move (it has nowhere to
> go), but the function call with return 2. Repeat indefinitely.
> 
> It's apparently an old bug, but it's been reported in
> https://github.com/company-mode/company-mode/issues/274 two days ago,
> because it causes an error in company-mode's popup rendering code when
> used together with a new-ish package.

Fixed in commit b544ab5 on the emacs-24 branch.

Thanks.