bug#42603: EWW shows chars > #xFF with font set by "set-fontset-font"

[Sebastian Urban]

Hello,

a quick recipe:
1. Open website in EWW with chars above #xFF, e.g.:
   M-x eww RET https://sjp.pl/slownik/ort/ RET
2. M-: (set-fontset-font t 'unicode "Times New Roman")
   ... or any font, other than in variable-pitch face
3. Watch as some chars change font.

The thing is, both unchanged and changed chars have face of
variable-pitch ("C-u C-x =" on char), so nothing should change,
I think.

Something similar happens in:
   M-x list-charset-chars RET unicode-bmp RET
#x00 -> #xFF stays the same, next segments change.

Tested on: GNU Emacs 28.0.50 (build 1, x86_64-w64-mingw32) of
2020-07-05.


S. U.