Query the mouse buttons initially in case the middle button was used

Change-Id: I99a3ef598bdaaba1afb6bf6521d1ceafcc9b603c
Reviewed-by: André de la Rocha <andre.rocha@qt.io>

src/plugins/platforms/windows/qwindowspointerhandler.cpp

@@ -579,7 +579,9 @@ bool QWindowsPointerHandler::translatePenEvent(QWindow *window, HWND hwnd, QtWin
 
     const QTabletEvent::TabletDevice device = QTabletEvent::Stylus;
     QTabletEvent::PointerType type;
-    Qt::MouseButtons mouseButtons;
+    // Since it may be the middle button, so if the checks fail then it should
+    // be set to Middle if it was used.
+    Qt::MouseButtons mouseButtons = queryMouseButtons();
 
     const bool pointerInContact = IS_POINTER_INCONTACT_WPARAM(msg.wParam);
     if (pointerInContact)