Hotspot not set in QML Drag

The QML Drag component doesn't set the hotspot when starting a drag.

Fix: set the hotspot in qquickdrag.cpp (in startDrag(), line 760) :

drag->setHotSpot(hotSpot.toPoint());

I tested it under Qt 5.9.1 / macOS 10.12, and should affect all versions and OS.