Fix: Some NWidget lists were not properly closed. (#11425)

(cherry picked from commit d4a77411a5)

src/bootstrap_gui.cpp

@@ -33,6 +33,7 @@
 /** Widgets for the background window to prevent smearing. */
 static const struct NWidgetPart _background_widgets[] = {
 	NWidget(WWT_PANEL, COLOUR_DARK_BLUE, WID_BB_BACKGROUND), SetResize(1, 1),
+	EndContainer(),
 };
 
 /**