Re: dxdiag: Do not omit mandatory argument to WriteFile.

[Lauri Kenttä]

I'm sorry if I missed something, but at least MSDN clearly states that 
this is usually an optional argument.

http://msdn.microsoft.com/en-us/library/windows/desktop/aa365747%28v=vs.85%2...

For example,
"lpNumberOfBytesWritten [out, optional]"
"Use NULL for this parameter if this is an asynchronous operation to 
avoid potentially erroneous results."
"This parameter can be NULL only when the lpOverlapped parameter is not 
NULL."