Fix authentication loss not handled correctly

This handles the case where on initial API connection, the server
responds with an `Unauthorized` response. It doesn't perform this same
checking/handling on every API request, which is probably what we want
eventually.

Opting to not address the full issue because I know this is going to be
a long one (see
https://github.com/ppy/osu/blob/05c50c0f6cfafab359963586ec265ad4f143a46c/osu.Game/Online/API/APIAccess.cs#L233).

osu.Game/Online/API/APIAccess.cs

@@ -148,6 +148,16 @@ private void run()
 
                         var userReq = new GetUserRequest();
 
+                        userReq.Failure += ex =>
+                        {
+                            if (ex.InnerException is WebException webException && webException.Message == @"Unauthorized")
+                            {
+                                log.Add(@"Login no longer valid");
+                                Logout();
+                            }
+                            else
+                                failConnectionProcess();
+                        };
                         userReq.Success += u =>
                         {
                             localUser.Value = u;
@@ -167,6 +177,7 @@ private void run()
                         // getting user's friends is considered part of the connection process.
                         var friendsReq = new GetFriendsRequest();
 
+                        friendsReq.Failure += _ => failConnectionProcess();
                         friendsReq.Success += res =>
                         {
                             friends.AddRange(res);