bug#50660: 28.0.50; Text artifacting when the cursor moves over text under mouse face that originally displayed a box

[Eli Zaretskii]

> From: Po Lu <luangruo@yahoo.com>
> Cc: larsi@gnus.org,  50660@debbugs.gnu.org
> Date: Fri, 24 Sep 2021 07:53:20 +0800
> 
> If the mouse face's box is set to something preposterous, like (:box
> 10000), the entire row is occluded by the box, and doesn't become
> visible again when canceling mouse face.  Only redraw-display makes the
> problem go away.

Emacs gives enough rope for Lisp programmers to hang themselves.  When
they try doing that, our only job is not to crash.  IOW, producing
preposterous display results for preposterous settings is justified;
we don't need to go out of our way to cater to ridiculous parameter
values like the one above, we only need to avoid crashing.