A second finger, a long touch or a cancelled contact replaced Drag::Art
with Drag::Gesture without ending the live Move interaction, which then
outlived the pointer: later edits began on top of an open interaction.
drop_press now cancels the move for Drag::Art too and clears the panel
payload, as it already did for Drag::Tool.
Test: a_second_finger_drops_a_move_waiting_over_a_panel.