bug#33017: 26.1; no update for displaying glyphless characters

[Eli Zaretskii]

> From: ynyaaa@gmail.com
> Date: Thu, 11 Oct 2018 23:37:13 +0900
> 
> 
> Evaluate the form below,
> characters are displayed as boxed hex numbers.
> 
> (dotimes (i 1000)
>   (insert (+ #x100000 i) ?\n))
> 
> Then type C-v or M-v to scroll up or down.
> In some positions of the window, hex numbers for characters are
> not updated.
> 
> For example, just after evaluation, [1003D7] is displayed on the top line.
> Typing M-v repeatedly, [1003D7] remains displayed on the top line.

Thanks, fixed on the emacs-26 branch.

For the record, this has been broken since Emacs 24.4.