Called as the first operation of the handOverTo function. 

This function allows custom classes to populate the new object. For surfces (this custom class) this function restores previously lost attributes. 

Overriding this function in a child class allows a child instance to be notified each time an object is handed over. 

This function is notified just before an object is to be handed over; giving this function the ability to cancel the handover. 

When overriding this function:

1. If the OdDbObject's state is incorrect, throw exception.
2. Call parent class's subHandover().
3. If other actions are required before handover, do them.

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