gestureswipe: Count last event when calculating velocity

gestureswipe: Count last event when calculating velocity

The last event, matching lifting the finger/releasing the mouse button,
is important when there's a large delay between it and the previous events,
as in when performing a movement, stopping, then releasing fingers as
opposed to doing a swipe.

If this event is skipped, doing this will result in kinetic deceleration
matching the previous finger movement, while the expected behavior would
be no deceleration.

See also 5dc6194b98792d937c648835cfadbe64977db443 for a similar fix in
GtkEventControllerScroll.