Called as the first operation as this object is being closed, for database -resident objects only.

This function is notified just before the current open operation is to be closed, giving this function the ability to perform necessary operatons. 

When overriding this function: 

1) If the OdDbObject's state is incorrect, throw exception. 

2) Call parent class's subClose(). 

3) If other actions are required before close, do them. 

The default implementation of this function does nothing. This function can be overridden in custom classes.