windows: always creating paging mapping, not file mapping

[dimichgh]

https://github.com/ozra/mmap-io/blob/master/src/mman.h#L57

Should it be as follows?

HANDLE h = (fd != -1) ? HANDLE(_get_osfhandle(fd)) : INVALID_HANDLE_VALUE;

But anyways, this will still be broken due to this problem: nodejs/node#6369

[ozra]

Better see if @toxicwolf has some input on it. I've been running Linux for 19 years, so I'm lost here B-) PR's are welcome.

[ozra]

Fixed via bkmartinjr, #11