explicitly set param2 to 0 in existing *DO_VTOL_TRANSITION commands. add a guard against NaNs.

src/modules/navigator/mission_block.cpp

@@ -699,6 +699,7 @@ MissionBlock::set_land_item(struct mission_item_s *item, bool at_current_locatio
 		vehicle_command_s vcmd = {};
 		vcmd.command = NAV_CMD_DO_VTOL_TRANSITION;
 		vcmd.param1 = vtol_vehicle_status_s::VEHICLE_VTOL_STATE_MC;
+		vcmd.param2 = 0.0f;
 		_navigator->publish_vehicle_cmd(&vcmd);
 	}
 
@@ -748,6 +749,7 @@ MissionBlock::set_vtol_transition_item(struct mission_item_s *item, const uint8_
 {
 	item->nav_cmd = NAV_CMD_DO_VTOL_TRANSITION;
 	item->params[0] = (float) new_mode;
+	item->params[1] = 0.0f;
 	item->yaw = _navigator->get_local_position()->heading;
 	item->autocontinue = true;
 }