Windows: Clear window under mouse in destruction of platform window.

Task-number: QTBUG-32042

Change-Id: I8aa5df84b7ca6deb47e0c3eff9a6a7d2c4793553
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>

src/plugins/platforms/windows/qwindowscontext.cpp

@@ -582,6 +582,11 @@ QWindow *QWindowsContext::windowUnderMouse() const
     return d->m_mouseHandler.windowUnderMouse();
 }
 
+void QWindowsContext::clearWindowUnderMouse()
+{
+    d->m_mouseHandler.clearWindowUnderMouse();
+}
+
 /*!
     \brief Find a child window at a screen point.
 

src/plugins/platforms/windows/qwindowscontext.h

@@ -166,6 +166,7 @@ public:
                                              unsigned cwex_flags) const;
 
     QWindow *windowUnderMouse() const;
+    void clearWindowUnderMouse();
 
     inline bool windowsProc(HWND hwnd, UINT message,
                             QtWindows::WindowsEventType et,

src/plugins/platforms/windows/qwindowsmousehandler.h

@@ -72,6 +72,7 @@ public:
 
     static Qt::MouseButtons queryMouseButtons();
     QWindow *windowUnderMouse() const { return m_windowUnderMouse.data(); }
+    void clearWindowUnderMouse() { m_windowUnderMouse = 0; }
 
 private:
     inline bool translateMouseWheelEvent(QWindow *window, HWND hwnd,

src/plugins/platforms/windows/qwindowswindow.cpp

@@ -871,6 +871,9 @@ void QWindowsWindow::destroyWindow()
         qDebug() << __FUNCTION__ << this << window() << m_data.hwnd;
     if (m_data.hwnd) { // Stop event dispatching before Window is destroyed.
         setFlag(WithinDestroy);
+        QWindowsContext *context = QWindowsContext::instance();
+        if (context->windowUnderMouse() == window())
+            context->clearWindowUnderMouse();
         if (hasMouseCapture())
             setMouseGrabEnabled(false);
         unregisterDropSite();
@@ -893,7 +896,7 @@ void QWindowsWindow::destroyWindow()
 #endif // !Q_OS_WINCE
         if (m_data.hwnd != GetDesktopWindow())
             DestroyWindow(m_data.hwnd);
-        QWindowsContext::instance()->removeWindow(m_data.hwnd);
+        context->removeWindow(m_data.hwnd);
         m_data.hwnd = 0;
     }
 }