DBStructDef :: IsUndefinedMember - Checks member for being undefined
Undefined structure members are those, that have been checked once with errors.
Return value:  Return value ( logical  )
The function returns YES when the question was answered positively. Otherwise it returns NO.
Implementation details
logical 
DBStructDef  :: IsUndefinedMember ( NString &prop_names )
- prop_names
 - Property name
The property name is passed as 0-terminated string. It may contain a property path that consists of a sequence of property names. 

