bug#25666: Screen rendering bug

[Eli Zaretskii]

> From: Fredrik Ljungdahl <fredde1994@gmail.com>
> Date: Thu, 9 Feb 2017 09:23:48 +0100
> 
> * I used a 146x46 size terminal (potentially matters)
> * Acquire this: http://sprunge.us/hVNi
> * Invoke emacs with emacs -Q
> * Go to this file (C-x C-f hVNi)
> * Invoke line number mode (M-x linum-mode), lack of linum-mode doesn't seem 
> to reproduce this
> * Split the window (C-x 3)
> * Hold down C-n (C-v does not reproduce this)
> * On the 2nd half-scroll, the 2nd split window should have its rendering 
> messed up in obvious ways

I did this, and didn't see any messup.