Always check for dragging changed, not just when movement starts

Otherwise, if you flick and then start a new drag before the flick
completes, dragging remains false.

Change-Id: I9bbe20107317a6edf765c87d2e0afe3e9e2618e9
Done-with: Aaron Kennedy <aaron.kennedy@jollamobile.com>
Reviewed-by: Alan Alpert (Personal) <416365416c@gmail.com>