Plane: In FBWB make target alt track current if soaring is enabled and suppressing throttle.

ArduPlane/navigation.cpp

@@ -313,9 +313,11 @@ void Plane::update_fbwb_speed_height(void)
         int32_t alt_change_cm = g.flybywire_climb_rate * elevator_input * dt * 100;
         change_target_altitude(alt_change_cm);
         
-        if (is_zero(elevator_input) && !is_zero(target_altitude.last_elevator_input)) {
+        if ((is_zero(elevator_input) && !is_zero(target_altitude.last_elevator_input)) ||
+            (g2.soaring_controller.is_active() && g2.soaring_controller.get_throttle_suppressed())) {
             // the user has just released the elevator, lock in
             // the current altitude
+            // or we're in soaring mode with throttle suppressed
             set_target_altitude_current();
         }