This is required because the default value is "" which tells the mqtt
server to delete the retained value.
This in turn means that applications that care about when the car is in
a unknown location will not get the retained value.
This is a bit different from all of the other values in
`@always_published`. For them "" is only published if the value is
unknown or an error occurred. So it makes sense to delete the retained
value.
In this case however, a value of "" generally means "the car is outside
any known geofence" which is a valid condition it itself, and it should
be retained.
There was speculation this might affect the shift_state, but
unfortunately this was not followed up with any evidence or details. #1912
There are any number of solutions that could be deployed here. The
advantage of this solution however is it is not going to break anything
unless you specifically define the TESLAMATE_DEFAULT_GEOFENCE variable.
Fixes: #1336
