DragHandler won't recognize a press as a start of a drag gesture even when dragThreshold property is explicitly set to zero.

This breaks the case where an item is programmed/animated to fly around, and user catches it using touch/mouse pointer and possibly starts dragging afterward.

Steps to reproduce:

Suppose there's an item which can be dragged. When drag handler becomes active, this item's position gets bound to the drag handler's centroid/offset/whatever.

1. Item flies under the cursor (for example, animated back to the original position from a previous incomplete drag).
2. User pressed left mouse button.
3. User moves mouse.

Expected behavior:

At step 2 the item freezes in place. At step 3 it follows mouse cursor.

Actual behavior:

At step 2 the item keeps moving to its whatever original position was. At step 3 as soon as the drag is detected (which in case of 0 threshold is as soon as mouse moves at least 1 pixel), the item suddenly jumps back to where it was pressed (because drag handler remembered its "press" location) and then starts following the mouse as usual.