DarkModeToggle: don't set schedule when updating from accountsservice

[danirabbit]

No description provided.

[ryonakano]

Hmm, I'm still facing the linked issue with this branch, even after installing it and rebooting…

[danirabbit]

@ryonakano oops sorry you're right. This doesn't fix #8. The issue this fixes instead is:

1. Open System Settings → Desktop → Appearance and select either Default at night or Dark during the day
2. Select "Sunset to sunrise" and see that the style changes from light to dark (or dark to light)

Without this branch:
3. Schedule gets reset to "Disabled" after the style changes

With this branch:
4. Schedule remains on "sunset to sunrise"

[zeebok]

This does fix the schedule reset you explained