os/user: User.GroupIds shouldn't error on users with no groups
On Windows, the User.GroupIds currently errors out if the user has no
groups. This is incorrect, as the user may not be a member of any groups
as demonstrated by the new TestGroupIdsTestUser test.
Cq-Include-Trybots: luci.golang.try:gotip-windows-amd64-longtest,gotip-windows-arm64
Change-Id: I436aa6214f2b98ef98dfb6064caec3d682b3f3d2
Reviewed-on: https://go-review.googlesource.com/c/go/+/606675 Reviewed-by: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: Alex Brainman <alex.brainman@gmail.com> Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>