app: Don't overzealously tab complete options
app: Don't overzealously tab complete options

If the user hasn't typed a '-', don't offer options in the tab
autocompletion. This is consistent with other linux commands, and less
messy.

Fixes https://github.com/flatpak/flatpak/issues/4753

flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak,flatpak/flatpak