Fixed a heap-use-after-free in SortByPTypeProcess. (#6326)

The process incorrectly deleted original meshes from the scene when cleaning up after an error if those meshes had been added to its output list (outMeshes). The fix ensures proper ownership transfer by nullifying the original mesh pointer in the scene (pScene->mMeshes[i] = nullptr;) when the mesh is moved to outMeshes. This prevents the scene destructor from attempting to delete the mesh again later, while allowing the error cleanup path in SortByPTypeProcess to correctly delete all meshes it owns (both newly created and transferred originals).

Co-authored-by: Kim Kulling <kimkulling@users.noreply.github.com>

code/PostProcessing/SortByPTypeProcess.cpp

@@ -165,6 +165,7 @@ void SortByPTypeProcess::Execute(aiScene *pScene) {
             if (!(mConfigRemoveMeshes & mesh->mPrimitiveTypes)) {
                 *meshIdx = static_cast<unsigned int>(outMeshes.size());
                 outMeshes.emplace_back(mesh);
+                pScene->mMeshes[i] = nullptr; // Indicate ownership transfer
             } else {
                 delete mesh;
                 pScene->mMeshes[i] = nullptr;