fix McCready Speed calculation :
  wrong max speed to integer convertion and wrong exit loop condition

before this change, McSpeed max value is "absolute value of MaxSpeed (in m/s)" - 1m/s

it's critical bug for paragliders : error > 10% of max speed (3.6km/h to 7.8km/h)

TODO : use less speed step for MC Speed, for now we use 1m/s (3.6km/h)
  it's to huge for paraglider, common PG wing have only 10 to 15 km/h speed range.