R1:0ceb53bfae28

Fix issue where Git authentication would always 403 on non-public install.

Summary: This fixes an issue where Git authentication would always fail on an install with `policy.allow-public` set to false. This is because when public access is allowed, anonymous users can query the user list. However, when public access is not allowed, you have to be authenticated before you can read any of the user objects.

Test Plan:
Prior to this fix, I get:

```
james@james-laptop:~/git/8> git clone http://phabricator.