windows: handle ERROR_NOT_READY

windows: handle ERROR_NOT_READY

The windows-to-posix error translation doesn't include
ERROR_NOT_READY, add that.

Also add a default case that catches if we don't know what
an error is, and return EIO. That seems much safer than just
returning the Windows error directly, since the caller expects
an errno.

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