free map_sub_ before map_free(map_) to avoid UAF&&NullPtr bug mentioned in #4078 (#4079)

* free `map_sub_` before `map_free(map_)`

Signed-off-by: GoesM <GoesM@buaa.edu.cn>

* reformat

Signed-off-by: GoesM <GoesM@buaa.edu.cn>

---------

Signed-off-by: GoesM <GoesM@buaa.edu.cn>
Co-authored-by: GoesM <GoesM@buaa.edu.cn>

Author: 2 people

nav2_amcl/src/amcl_node.cpp

@@ -335,6 +335,7 @@ AmclNode::on_cleanup(const rclcpp_lifecycle::State & /*state*/)
   laser_scan_sub_.reset();
 
   // Map
+  map_sub_.reset();  //  map_sub_ may access map_, so it should be reset earlier
   if (map_ != NULL) {
     map_free(map_);
     map_ = nullptr;