Fix regression with docking from recents transition

Because we move the task to the front in startRecentsActivity, we
always overrode the app transition type. Instead, we should remove
this logic and keep a flag whether the animation was prolonging was
finished already. If it was finished already, don't start the
prolonging when starting the transition.

Bug: 27154882
Change-Id: I1cd9e323867726ebd4b131ed5c13c3834d0f1107