Showing an arrow for an empty expander row for the event confuses the user.
The user may misunderstand there is the information behind the arrow and then
the user will click it but will not get any response from the panel.
Therefore, to prevent confusing the user, the expander will be hidden for a
event with an empty description.
Fixes: https://gitlab.gnome.org/GNOME/gnome-control-center/-/issues/2031
Signed-off-by: Kate Hsuan <hpa@redhat.com>