Reads the .dwg file data of this object. 

eOk if reading was successful or an appropriate OdResult error code otherwise.

This function is called by dwgIn() to allow the object to read its data. When overriding this function:

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