Fix panel width sizing issue

SpritePacker-GUI/MainWindow.cs

@@ -50,7 +50,7 @@ namespace SpritePacker.GUI
 		private void setupWidgets()
 		{
 			// Create the layout containers
-			HBox masterContainer = new HBox(true, 10);
+			HBox masterContainer = new HBox(false, 10);
 			VBox leftPanel = new VBox(false, 0) { MarginRight = 5 };
 			VBox rightPanel = new VBox(false, 0) { MarginLeft = 5 };
 			Frame leftPanelFrame = new Frame("Sprites") { Child = leftPanel, Margin = 10, MarginRight = 5 };