On some xcb platforms the xcb_configure_notify_event_t is sent after the
window is fully exposed which leads to a wrong position for
QWidget::mapToGlobal() which makes the test fail.
Fix it by waiting for a move event with a position != 0,0 before
starting the drag'n'drop operation.
Fixes: QTBUG-94250
Change-Id: If91a15815205ba9dcea36248d9de03ed0a7e5822
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>