QAccessibleTabButton: fix isValid

The button interface is faking everything to represent the buttons when
it comes to accessibility, since they are not represented by a QWidget.
When the parent TabBar is in its destructor, isValid should return false
to prevent accessing it.

Task-number: QTBUG-69283
Change-Id: Ifedf3fa45f9106723afb0b04922b071a3c5467c3
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/widgets/accessible/complexwidgets.cpp

@@ -120,7 +120,14 @@ public:
         return rec;
     }
 
-    bool isValid() const override { return m_parent.data() && m_parent->count() > m_index; }
+    bool isValid() const override {
+        if (m_parent) {
+            if (static_cast<QWidget *>(m_parent.data())->d_func()->data.in_destructor)
+                return false;
+            return m_parent->count() > m_index;
+        }
+        return false;
+    }
 
     QAccessibleInterface *childAt(int, int) const override { return 0; }
     int childCount() const override { return 0; }

src/widgets/kernel/qwidget.h

@@ -714,6 +714,7 @@ private:
     friend class QWidgetWindow;
     friend class QAccessibleWidget;
     friend class QAccessibleTable;
+    friend class QAccessibleTabButton;
 #ifndef QT_NO_GESTURES
     friend class QGestureManager;
     friend class QWinNativePanGestureRecognizer;