Commits 4d1ffec and 6e481d0 renamed sub-ass-style-override to
sub-ass-override. But in commit bd603c2, when renaming it in
quit-watch-later's backup_properties, which determines which properties
are saved by quit-watch-later/write-watch-later-config, it was
incorrectly renamed to sub-style-override instead, and thus never got
saved even if modified at runtime. Instead mpv attempted to save the
non-existing property "sub-style-override", but since no error is raised
when saving non-existing properties with quit-watch-later, no one
noticed it. This commit renames the saved property to the correct new
name "sub-ass-override" so that it does get saved.
5e23e81485