ntdll: remove an unnecessary NULL check : Coverity

[Jeff L]

Dmitry Timoshkov wrote:
>
> 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.
>
Thanks for that, I will see what I can do about creating a suitable test.

Jeff