Make Redshift remember the last discovered location at startup

[z0mb1e-kgd]

Is your feature request related to a problem? Please describe.

When using GeoClue as the location provider, if you reboot the machine, it always takes ~ 20 - 30 seconds before GeoClue discovers the location and Redshift kicks in. It is always an eyes burning experience if this happens at night time.

Describe the solution you'd like

It would be great if Redshift would remember the last location provided by GeoClue, and update the location if it had changed once GeoClue discovers the location.