Fix scroll offsets

This is not a full fix, it merely restores the functionality
already present. The ScrollPanelWidget does not work right if
Align is set to Bottom but ScrollToBottom() isn't called after
adding items and there's not enough content to scroll.

OpenRA.Game/Widgets/ScrollPanelWidget.cs

@@ -151,7 +151,7 @@ namespace OpenRA.Widgets
 
 		public bool ScrolledToBottom
 		{
-			get { return ListOffset == Math.Min(0, Bounds.Height - ContentHeight); }
+			get { return ListOffset == Math.Min(0, Bounds.Height - ContentHeight) || ContentHeight <= Bounds.Height; }
 		}
 
 		public void ScrollToItem(string itemKey)