Plane: don't do throttle nudge while in geofence failsafe

user stick inputs should not apply when outside fence

ArduPlane/radio.cpp

@@ -188,7 +188,7 @@ void Plane::read_radio()
 
     channel_throttle->servo_out = channel_throttle->control_in;
 
-    if (g.throttle_nudge && channel_throttle->servo_out > 50) {
+    if (g.throttle_nudge && channel_throttle->servo_out > 50 && geofence_stickmixing()) {
         float nudge = (channel_throttle->servo_out - 50) * 0.02f;
         if (ahrs.airspeed_sensor_enabled()) {
             airspeed_nudge_cm = (aparm.airspeed_max * 100 - g.airspeed_cruise_cm) * nudge;