Remove overscroll on running task when it's not attached to RecentsView

This allows the running task to follow the finger freely until motion
pause is detected (or when trying to quick switch in a direciton that
has no tasks, as RecentsView is still attached until you swipe up).

Bug: 149934536
Change-Id: If68166e962af9f28c56017838f720e15ddb96560
2 files changed