os: support reading empty root directories on Windows

GetFileInformationByHandleEx can return `ERROR_FILE_NOT_FOUND` when no
files were found in a root directory, as per MS-FSA 2.1.5.6.3 [1].

This error code should not be treated as an error, but rather as an
indication that no files were found, in which case `readdir` should
return an empty slice.

This CL doesn't add any test as it is difficult to trigger this error
code. Empty root directories created using Windows utilities such as
`net use` always report at least the optional `.` and `..` entries.
A reproducer is provided in #61159, but it requires WinFSP to be
installed.

Fixes #61159

[1] https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-fsa/fa8194e0-53ec-413b-8315-e8fa85396fd8

Change-Id: Id46452030f5355c292e5b0abbf5e22af434a84d2
Reviewed-on: https://go-review.googlesource.com/c/go/+/507775
Reviewed-by: Nick Craig-Wood <nickcw@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>

0 files changed, 0 insertions, 0 deletions