Previously we ignored when we had no output configuration
**and** failed to apply the automatically created one.
This leads to two problems:
- If this happens on startup, we end up with no outputs being added to the shell and we quit.
- If this happens later, we might end up in an inconsistent state, where the shell thinks we have an output, when it didn't light up for similar reasons.
Thus `read_outputs` is failable and handling that very much depends on
the where is was called from, because `read_outputs` doesn't know what
configuration was active before.
Thus make it failable and provide useful mitigations everywhere
possible:
- Try to enable just one output in case we fail on startup.
- Don't enable any additional outputs, when we fail on hotplug.
- Log the error like previously in any other case (and come up with more
mitigations, once we understand these cases better).
