Set the prefs-value alongside the button status

Previous code just set the button-"status" based on what we stored on
the settings. This sets the corresponding value in our prefs-struct.

This fixes the same issue as in 63f7f3, without the side effect of
magically hiding the mean depth line.

Signed-off-by: Anton Lundin <glance@acc.umu.se>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>