Ensure costmap_2d_cloud does not seg fault on SIGINT.

One of several clean shutdown issues being address via Issue ros-navigation#3271.

Signed-off-by: mbryan <matthew.bryan@dell.com>

Author: mbryan

nav2_costmap_2d/src/costmap_2d_cloud.cpp

@@ -225,6 +225,11 @@ int main(int argc, char ** argv)
     "voxel_grid", rclcpp::SystemDefaultsQoS(), voxelCallback);
 
   rclcpp::spin(g_node->get_node_base_interface());
+
+  g_node.reset();
+  pub_marked.reset();
+  pub_unknown.reset();
+
   rclcpp::shutdown();
 
   return 0;