Plane: reset baro_takeoff_alt while disarmed

ArduPlane/takeoff.cpp

@@ -18,6 +18,7 @@ bool Plane::auto_takeoff_check(void)
     // reset all takeoff state if disarmed
     if (!hal.util->get_soft_armed()) {
         memset(&takeoff_state, 0, sizeof(takeoff_state));
+        auto_state.baro_takeoff_alt = barometer.get_altitude();
         return false;
     }