Fix tap-through during screenshot dismissal

We were removing the onComputeInternalInsetsListener at the start
of the dismissal animation, which broke tap-through during
dismissal. We remove the listener after dismissal anyway, so just
wait until then.

Bug: 191981223
Bug: 191981223
Test: manual (helps to have window animation scale (slow) on)
Change-Id: I4cbf9376f8646904ed991aec55faeb271826684a