transaction: Only allow to run once
transaction: Only allow to run once

Currently, the code will happily run an already-executed
transaction again, with dubious outcomes. Just prevent
this from happening.

Closes: #2195
Approved by: alexlarsson

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