Any press during a drag abandoned it with `OnDragStop`, so touching the right button while dragging an item or a window with the left stopped the drag.
In the reference, each press on the capture runs the drag arm: a button in the frame's drag mask re-arms it, started back to 0, with no `OnDragStop`, and any other button leaves the drag running. The release of a button in the mask ends a started drag with `OnDragStop`, or disarms an unstarted one. `OnDragStart` names the lowest held button.
Presses now re-arm or leave the drag as the reference does, the release tests the released button against the mask, and `OnDragStart` names the lowest held button. A release the client lost still stops the drag.
Tests cover a right press on a left-only drag, a re-arm, the first release after it, an item drag and the start's button.
Fixes#924
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
