select_nearest_aircraft passes altitudeM: null for an airborne contact
without a barometric altitude (military rows from adsb.lol can lack
alt_baro). The speech builder coerced it with Number(), and Number(null)
is 0, so the reply said "..., 0 feet." and the voice card showed
"Altitude 0 feet". Read the altitude only when it is a finite number,
so an unknown one is left out as the builder already intends.
Aditya
ea1b0d8d55