The layer bar Quick Offset was followed and ended in its row's code, and
rows out of view aren't drawn. Released with its row scrolled away, it
stayed active: the next drag of that bar, even a plain one, ran as a
Quick Offset from the old origin, into the old undo step.
Like the key drag, it now follows the pointer below the rows and ends
when the button is released, wherever the bar's row is.
Test: a_quick_offset_released_off_screen_ends (release with the row
scrolled away; a plain drag after it moves both layers together as its
own undo step; fails before).
tylerjenningsw
bfb7507565