bug#35273: "Marker does not point anywhere" when reading next article

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@gmail.com>
> Cc: contovob@tcd.ie,  35273@debbugs.gnu.org,  leah@vuxu.org
> Date: Sat, 27 Apr 2019 15:28:01 -0400
> 
> > OK, thanks.  Then I think it would be better to test the overlay for
> > being dead in xdisp.c, before we call mouse_face_overlay_overlaps.
> > Also, a faster test would be to check that the marker's buffer is a
> > NULL pointer, doing that doesn't require a call marker-position.
> > WDYT?
> 
> Sure, that works.  Should I push to emacs-26?

Yes, please.