ntdll: remove an unnecessary NULL check : Coverity

[Dmitry Timoshkov]

"Jeff L" <lats at yless4u.com.au> wrote:

> Looking a bit further it seems that NtCreateMailslotFile is only called 
> from CreateMailslotW.  If there is a problem with a NULL then it stems 
> from there. <http://source.winehq.org/ident?i=CreateMailslotW>

NtCreateMailslotFile is a public API, so probably it should handle the case
when attr is NULL. I see the same problem at least in NtCreateNamedPipeFile.
In general, handling of OBJECT_ATTRIBUTES in ntdll is not consistent, but
fixing it properly most likely a test is needed to see what Windows does
in that case.

-- 
Dmitry.