Fix issue #5149: Make chat window not autoscroll

It will autoscroll unless the chat window is open and the scroll
position is not at the bottom.

OpenRA.Mods.RA/Widgets/Logic/IngameChatLogic.cs

@@ -146,8 +146,11 @@ namespace OpenRA.Mods.RA.Widgets.Logic
 				template.Bounds.Height += dh;
 			}
 
+			bool scrolledToBottom = chatScrollPanel.ScrolledToBottom;
 			chatScrollPanel.AddChild(template);
+			if (scrolledToBottom)
 				chatScrollPanel.ScrollToBottom();
+
 			Sound.PlayNotification(null, "Sounds", "ChatLine", null);
 		}
 	}