bug#20701: 25.0.50; [PATCH] (vertical-motion 0) broken at display strings after newline

[Eli Zaretskii]

> Cc: Eli Zaretskii <eliz@gnu.org>
> From: Wolfgang Jenkner <wjenkner@inode.at>
> Date: Sun, 31 May 2015 16:19:46 +0200
> 
> If you run the following snippet in emacs -Q point will end up at the
> first line of the "Test" buffer, but it should stay at the second line.
> 
> (with-current-buffer (generate-new-buffer "Test")
>   (pop-to-buffer (current-buffer))
>   (insert "x\n")
>   (save-excursion
>     (insert (propertize "x" 'display "x")))
>   (sit-for 1)
>   (vertical-motion 0))
> 
> On the other hand, non-zero arguments for vertical-motion seem to work
> correctly, as long as the buffer contains only ASCII characters before
> the propertized "x".
> 
> Otherwise
> 
> (with-current-buffer (generate-new-buffer "Test")
>   (pop-to-buffer (current-buffer))
>   (insert "\né\n")
>   (save-excursion
>     (insert (propertize "x" 'display "x")))
>   (sit-for 1)
>   (vertical-motion -1))
> 
> Here, point should go to the second line but it goes to the first line.
> 
> The following patch tries to fix both issues.
> 
> -- >8 --
> Subject: [PATCH] * src/indent.c (Fvertical_motion): Fix a case of motion by 0
>  lines.
> 
> Starting from a display string after a newline, point went to the
> previous line.
> 
> Also, correct an inadvertent use of a buffer position with FETCH_BYTE.

Looks good to me, please push.

Thanks.