bug#26852: 25.2; C-n may not keep column

[Eli Zaretskii <eliz@gnu.org>]

> From: ynyaaa@gmail.com
> Date: Tue, 09 May 2017 19:56:45 +0900
> 
> 
> Evaluate the form below and resize frame
> to hide the lower half of the window bottom line.
> (hide digits and show the upper half of "X")
> 
> Then input C-n repeatedly to move down.
> Each time the buffer is scrolled up,
> the column of the cursor position moves right.
> 
> (let ((buf (generate-new-buffer "*tmp*"))
>       (line (concat (propertize "X" 'face '(:height 5.0))
> 		    "01234567890123456789\n")))
>   (switch-to-buffer buf)
>   (dotimes (i 100)
>     (insert (format "%2d " i) line))
>   (goto-char (point-min))
>   (forward-char 4))

Thanks, I fixed this.