Returns size of the private storage byte array. 
This can only be called on a DOFCredentials that has been constructed.
- Parameters
 - 
  
    | self | The credentials. This must not be NULL. | 
  
   
- Returns
 - The size of the private storage byte array. 
 
- Exceptions
 - 
  
    | 0 | is returned if the credentials do not contain the private storage information. | 
  
   
- See Also
 - DOFCredentials_GetPrivateStorage