This adds a flight task to catch the case where we want to do an
emergency descent without GPS but only a baro.
Previously, this would lead to the navigator land class being called
without position estimates which then made the flight tasks fail and
react with a flight task failsafe. This however meant that landed was
never detected and a couple of confusing error messages.
This applies if NAV_RCL_ACT is set to 3 "land".