Fix regression with the closing task leash visibility

- We should actually be showing the transition leash if it was
  previously closing and not hiding it
- There's another case where we hide the opening task surface when
  setting up for the transition, we need to also override this alpha
  if the task was previously visible

Bug: 296242449
Test: Quickswitch quickly between tasks such that we relaunch a pausing/
      closed task
Change-Id: I1416eb261ba9016174f1deefd293d58f64ab05ed