Fix a label width size issue.

UICatalog/Scenarios/DynamicMenuBar.cs

@@ -143,7 +143,7 @@ namespace UICatalog.Scenarios {
 					TextAlignment = TextAlignment.Centered,
 					X = Pos.Right (_btnPrevious) + 1,
 					Y = Pos.Top (_btnPrevious),
-					Width = Dim.Fill () - Dim.Width (_btnAdd) - 1,
+					Width = Dim.Fill () - Dim.Function (() => _btnAdd.Frame.Width + 1),
 					Height = 1
 				};
 				_frmMenu.Add (_lblMenuBar);