Stop adding users on PRESENCE_UPDATE

src/Discord.Net/DiscordClient.cs

@@ -902,7 +902,7 @@ namespace Discord
                                     break;
                                 }
                                 else
-                                    user = server.AddUser(data.User.Id);
+                                    user = server.GetUser(data.User.Id);
                             }
 
                             if (user != null)

src/Discord.Net/Models/Server.cs

@@ -456,8 +456,8 @@ namespace Discord
             
             if (_users.TryGetOrAdd(id, member, out member))
             {
-                foreach (var channel in AllChannels)
-                    channel.AddUser(member.User);
+                foreach (var channel in _channels)
+                    channel.Value.AddUser(member.User);
             }
             return member.User;
         }
@@ -467,8 +467,8 @@ namespace Discord
             Member member;
             if (_users.TryRemove(id, out member))
             {
-                foreach (var channel in AllChannels)
-                    channel.RemoveUser(id);
+                foreach (var channel in _channels)
+                    channel.Value.RemoveUser(id);
                 return member.User;
             }
             return null;