Reads the DGN data of this object. 

Returns the filer status.

This function is called by dgnIn() to allow the object to read its data. 

When overriding this function: 

1) Call assertWriteEnabled(). 2) Call the parent class's dgnInFields(pFiler). 3) If it returns eOK, continue; otherwise return whatever the parent's dgnInFields(pFiler) returned. 4) Call the OdDgFiler(pFiler) methods to read each of the object's data items in the order they were written. 5) Return pFiler->filerStatus().