Fix #144483: Use-after-free when splitting View3D opened Asset Shelf

`asset_shelf::regiondata_duplicate()` first creates a shallow copy of
the `AssetShelf`, including its `AssetShelfSettings` member. So the
contained pointer point to the same memory.

While this is a rather unusual case for a copy assignment operator to
consider, I think this is fine since the API allows these shadow copies.
This is a bit of a consequence of mixing C and C++ style memory
management.

Pull Request: https://projects.blender.org/blender/blender/pulls/144613

source/blender/blenlib/BLI_listbase.h

@@ -395,6 +395,10 @@ BLI_INLINE bool operator==(const ListBase &a, const ListBase &b)
 {
   return BLI_listbase_equal(&a, &b);
 }
+BLI_INLINE bool operator!=(const ListBase &a, const ListBase &b)
+{
+  return !(a == b);
+}
 
 template<typename T, typename Fn> T *BLI_listbase_find(const ListBase &listbase, Fn &&predicate)
 {

source/blender/editors/asset/intern/asset_shelf_settings.cc

@@ -41,9 +41,14 @@ AssetShelfSettings &AssetShelfSettings::operator=(const AssetShelfSettings &othe
     return *this; /* Handle self-assignment safely. */
   }
 
-  /* Free existing properties. */
-  BKE_asset_catalog_path_list_free(this->enabled_catalog_paths);
-  MEM_SAFE_FREE(this->active_catalog_path);
+  /* Free existing properties. Check if they point to the same memory first, #AssetShelfSettings
+   * might have been shallow copied before. */
+  if (this->enabled_catalog_paths != other.enabled_catalog_paths) {
+    BKE_asset_catalog_path_list_free(this->enabled_catalog_paths);
+  }
+  if (this->active_catalog_path != other.active_catalog_path) {
+    MEM_SAFE_FREE(this->active_catalog_path);
+  }
 
   /* Copy from 'other'. */
   this->asset_library_reference = other.asset_library_reference;