Fix crash in TWidgetHelper::show/hideChildren.

ui/rp_widget.cpp

@@ -12,6 +12,30 @@
 #include <QtGui/QtEvents>
 
 namespace Ui {
+namespace {
+
+[[nodiscard]] std::vector<QPointer<QWidget>> GetChildWidgets(
+		not_null<QWidget*> widget) {
+	const auto &children = widget->children();
+	auto result = std::vector<QPointer<QWidget>>();
+	result.reserve(children.size());
+	for (const auto child : children) {
+		if (child && child->isWidgetType()) {
+			result.push_back(static_cast<QWidget*>(child));
+		}
+	}
+	return result;
+}
+
+} // namespace
+
+void ToggleChildrenVisibility(not_null<QWidget*> widget, bool visible) {
+	for (const auto &child : GetChildWidgets(widget)) {
+		if (child) {
+			child->setVisible(visible);
+		}
+	}
+}
 
 void ResizeFitChild(
 		not_null<RpWidget*> parent,

ui/rp_widget.h

@@ -18,6 +18,12 @@
 #include <QtCore/QPointer>
 #include <QtGui/QtEvents>
 
+namespace Ui {
+
+void ToggleChildrenVisibility(not_null<QWidget*> widget, bool visible);
+
+} // namespace Ui
+
 class TWidget;
 
 template <typename Base>
@@ -30,18 +36,10 @@ public:
 	}
 
 	void hideChildren() {
-		for (auto child : Base::children()) {
+		Ui::ToggleChildrenVisibility(this, false);
-			if (child->isWidgetType()) {
-				static_cast<QWidget*>(child)->hide();
-			}
-		}
 	}
 	void showChildren() {
-		for (auto child : Base::children()) {
+		Ui::ToggleChildrenVisibility(this, true);
-			if (child->isWidgetType()) {
-				static_cast<QWidget*>(child)->show();
-			}
-		}
 	}
 
 	void moveToLeft(int x, int y, int outerw = 0) {