Remove one more unnecessary initialization of std::unique_ptr in a constructor.
Remove one more unnecessary initialization of std::unique_ptr in a constructor.

opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core,opensim-org/opensim-core