Blender Git Loki

Fix T72499: UV Editor : Selection tools don't deselect when dragging on an empty space [face selection]

If pre-deselecting takes place, then flushing was not happening
('changed' never became true because no new faces were being selected).

This rectifies the logic. (also removed redundant double initialization
to false)

Maniphest Tasks: T72499

Differential Revision: https://developer.blender.org/D6459