Fix #14756: Invalidate nested focus before widget container is cleared. (#14809)

src/widget.cpp

@@ -3476,3 +3476,20 @@ std::unique_ptr<NWidgetBase> MakeCompanyButtonRows(WidgetID widget_first, Widget
 	if (hor != nullptr) vert->Add(std::move(hor));
 	return vert;
 }
+
+/**
+ * Unfocuses the focused widget of the window,
+ * if the focused widget is contained inside the container.
+ * @param parent_window Window which contains this container.
+ */
+void NWidgetContainer::UnfocusWidgets(Window *parent_window)
+{
+	assert(parent_window != nullptr);
+	if (parent_window->nested_focus != nullptr) {
+		for (auto &widget : this->children) {
+			if (parent_window->nested_focus == widget.get()) {
+				parent_window->UnfocusFocusedWidget();
+			}
+		}
+	}
+}