evdevtouch: Avoid crashing on exit

26238aca8c442736f380eb523ef48468f892bdb7 causes double deletion of the
QTouchDevice in case the post routine already cleaned up the list by the
time the touch handler gets to do it.

Just check the list of devices to see if the one we hold is still there.
If not, the pointer is likely to be a dangling one so do nothing.

This will avoid dying with bus error or similar on application exit.

Task-number: QTBUG-51562
Change-Id: I50c1edee7405aad308274538219698388c2cc9f9
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

src/gui/kernel/qwindowsysteminterface.cpp

@@ -442,6 +442,11 @@ void QWindowSystemInterface::unregisterTouchDevice(const QTouchDevice *device)
     QTouchDevicePrivate::unregisterDevice(device);
 }
 
+bool QWindowSystemInterface::isTouchDeviceRegistered(const QTouchDevice *device)
+{
+    return QTouchDevicePrivate::isRegistered(device);
+}
+
 void QWindowSystemInterface::handleTouchEvent(QWindow *w, QTouchDevice *device,
                                               const QList<TouchPoint> &points, Qt::KeyboardModifiers mods)
 {

src/gui/kernel/qwindowsysteminterface.h

@@ -123,6 +123,7 @@ public:
 
     static void registerTouchDevice(const QTouchDevice *device);
     static void unregisterTouchDevice(const QTouchDevice *device);
+    static bool isTouchDeviceRegistered(const QTouchDevice *device);
     static void handleTouchEvent(QWindow *w, QTouchDevice *device,
                                  const QList<struct TouchPoint> &points, Qt::KeyboardModifiers mods = Qt::NoModifier);
     static void handleTouchEvent(QWindow *w, ulong timestamp, QTouchDevice *device,

src/platformsupport/input/evdevtouch/qevdevtouchhandler.cpp

@@ -393,9 +393,13 @@ void QEvdevTouchScreenHandler::unregisterTouchDevice()
     if (!m_device)
         return;
 
-    QWindowSystemInterface::unregisterTouchDevice(m_device);
+    // At app exit the cleanup may have already been done, avoid
+    // double delete by checking the list first.
+    if (QWindowSystemInterface::isTouchDeviceRegistered(m_device)) {
+        QWindowSystemInterface::unregisterTouchDevice(m_device);
+        delete m_device;
+    }
 
-    delete m_device;
     m_device = Q_NULLPTR;
 }