A GAppInfo is not guaranteed to have a filename or an application (or
rather a desktop ID). Add a check for application_id to be non-NULL
before trying to call sn_launcher_set_application_id, which would crash
otherwise.
https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1392
Calculations were being done at places accounting on usec precision,
however those are still treated as having msec precision at places. Let's
consolidate for the latter since it requires less changes across the board
and usec precision doesn't buy us anything here.
Closes: https://gitlab.gnome.org/GNOME/mutter/issues/541
