Flicking TreeView with touchscreen does not work as QTouchDevice::devices() is empty

 Flicking a QML `TreeView` does not work possibly because `Settings.hasTouchScreen` returns `false`. This seems to be due to the fact that `QTouchDevice::devices()` is empty.

I put the following code in `main()` of the standard Qt example:

https://doc.qt.io/qt-5/qtquickcontrols1-filesystembrowser-example.html:

const auto devices = QTouchDevice::devices();
 qDebug() << "************** devices.length(): " << devices.length();

for (const QTouchDevice *dev : devices)
 qDebug() << "**************** dev->type():" << dev->type();

The `length()` returned is 0, although the touchscreen is working with that example. Selection, button press, etc. all work, but the list cannot be flicked.

I am using tslib on the latest Raspbian.