Improve details mode ctrl-press rubberband creation
Since d3839617 dragging the highlighted row of already selected items in the details view mode will begin a drag operation of all selected items.
As a unintended side-effect of this change, dragging the row of a previously unselected item while holding the control key would also begin a drag operation.
After this commit, dragging the row of a previously unselected item while holding the control key in details view mode will instead create a rubberband. Ctrl-dragging the item's icon or text directly will drag the item as expected.
With this change, using multiple rubberbands to select scattered items among a list of items should be as convenient as it was previously.