bug#43469: 28.0.50; window-text-pixel-size returns incorrect value when line-prefix is set

[Eli Zaretskii]

> From: Yuan Fu <casouri@gmail.com>
> Date: Thu, 17 Sep 2020 12:03:35 -0400
> 
> (progn (insert "xxxxxxxxxxxxxx")
>        (print (car (window-text-pixel-size
>                     nil (line-beginning-position) (line-end-position))))
>        (put-text-property (line-beginning-position) (line-end-position)
>                           'line-prefix "   ")
>        (print (car (window-text-pixel-size
>                     nil (line-beginning-position) (line-end-position)))))
> 
> Prints first 98, then 119

Why do you think this is a bug?