I guess the changes that involved `MultiplayerTestScene` having a test
user lookup cache caused this test case to false-pass silently.
Added an explicit assert which ensures the added user indeed has a null
`User` value.
The fix here is correcting the access of `user.Country`. The deicision
to have null users display is because this is the best we can do (if
osu-web could not resolve the user). We still want the users in the
lobby to be aware of this user's presence, rather than hiding them from
view.
osu-stable does a similar thing, showing these users as `[Loading]`. I
decided to go with blank names instead because having *any* text there
causes confusion. We can iterate on this in future design updates.
