[PATCH 3/4] ntdll: Partially implement NtCancelSynchronousIoFile.

[Daniel Lehman]

> If io is specified, it should never cancel any I/O operations other than the one specified by the parameter.
>
> Better keep returning STATUS_NOT_IMPLEMENTED in this case?
>

i'm not entirely sure how it's used.  for the synchronous case where
it does cancel, passing a non-null io returns c0000225 (NOT_FOUND)
instead of canceling.  i don't see any difference in the asynchonous
test case that already returns that

returning c0000225 for a non-null io would at least match windows, but
feels like a fixme would still be needed since i'd still be ignoring
it

the io didn't make any difference for implementing CancelSynchronousIo
in kernelbase, which was what i was going for.  and since it's more
documented, CancelSynchonousIo is more likely to be called than
NtCancelSynchronousIoFile directly

i can certainly add more tests to probe it, though, if preferred

thanks
daniel