When we initially turned on admin sidebar for new sites,
existing sites had the value set to -1. We need to show
the problem check to these sites too, but currently it only
checks if `admin_sidebar_enabled_groups` is empty.
We want to avoid surprises when we make the new admin sidebar baseline, so in addition to announcements, we're also adding a problem check that informs you if you don't have it enabled for any group yet.
