override: Don't fail completion on empty repos
override: Don't fail completion on empty repos

This lets completion keep working after you type
flatpak override --installation=empty

Closes: #2585
Approved by: alexlarsson

flatpak/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,flatpak/flatpak