Fix invalid positioning when basket is scrolled

When basket got scrolled down or right itemAt(enent->screenPos()) method treats screenPos() as coordinates from the absolute topleft corner of the view not the scrolled one. So when basket is scrolled and user starts selecting text inside editor, note dragging starts instead.

This bug can be observed at the "Tips" basket as it scrolled a bit.
(previous version mistakenly used QPointF)