Finding peace with the UI thread.

There is the issue that in some cases that the ui thread blocked.

osu.Game/Overlays/Chat/ChatTabControl.cs

@@ -49,7 +49,9 @@ namespace osu.Game.Overlays.Chat
 
         public void AddItem(Channel channel)
         { 
+            if (!ChannelTabControl.Items.Contains(channel))
                 ChannelTabControl.AddItem(channel);
+
             if (Current.Value == null)
                 Current.Value = channel;
         }

osu.Game/Overlays/Chat/DrawableChannel.cs

@@ -55,15 +55,11 @@ namespace osu.Game.Overlays.Chat
             Channel.PendingMessageResolved += pendingMessageResolved;
         }
 
-        [BackgroundDependencyLoader]
-        private void load()
-        {
-            newMessagesArrived(Channel.Messages);
-        }
-
         protected override void LoadComplete()
         {
             base.LoadComplete();
+
+            newMessagesArrived(Channel.Messages);
             scrollToEnd();
         }
 

osu.Game/Overlays/Chat/Selection/ChannelSelectionOverlay.cs

@@ -124,6 +124,8 @@ namespace osu.Game.Overlays.Chat.Selection
         }
 
         public void UpdateAvailableChannels(IEnumerable<Channel> channels)
+        {
+            Scheduler.Add(() =>
             {
                 sectionsFlow.ChildrenEnumerable = new[]
                 {
@@ -142,6 +144,7 @@ namespace osu.Game.Overlays.Chat.Selection
                         c.OnRequestLeave = channel => { OnRequestLeave?.Invoke(channel); };
                     }
                 }
+            });
         }
 
         [BackgroundDependencyLoader]