windowsaio: fix file offset bug

I was monitoring file IO while running fio today and noticed that the file
offset when using windowsaio was always 0.
Because the OVERLAPPED structure contains a union, by initializing Pointer
to NULL the code was also overwriting the Offset field.
I've attached a patch that fixes it.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
1 file changed