Fix display of empty margins when default face is remapped

Fix display of empty margins when default face is remapped

* src/xdisp.c (display_line): Append space glyphs to margin areas
if the default face is remapped and nothing is written to the
margin area of this screen line.
(produce_special_glyphs): If the truncation/continuation glyphs do
not specify a face, use the remapped default face, not the
original frame-global default face.  Reported by Nicolas
P. Rougier <nicolas.rougier@inria.fr> in
https://lists.gnu.org/archive/html/emacs-devel/2024-07/msg01217.html.

(cherry picked from commit 80108438e5e2e95ca75e59212fb1669a723241b5)