omitted optional integer fields parsed as 0

[derhuerst]

TripUpdate.decode(TripUpdate.encode({trip: {trip_id: '1'}}))

{
  trip: {
    trip_id: '1',
    route_id: '',
    direction_id: 0,
    start_time: '',
    start_date: '',
    schedule_relationship: 0
  },
  vehicle: null,
  stop_time_update: [],
  timestamp: 0,
  delay: 0
}

This will lead to unintentionally wrong processing of e.g. delay downstream.

[derhuerst]

This is due to mafintosh/protocol-buffers#20.

[derhuerst]

Should be fixed because derhuerst/gtfs-rt-bindings#6 is fixed.