Fix some crashes when going between fold / unfold with bubble bar

There were two issues here:
1 - that the current task view listener could be unset, so check for
    that and use the value on the bubbleTaskView in that case.
2 - the post delay call we have assumes that we'll have stackview, which
    is the case in prod, but not with bubble bar.

Flag: EXEMPT trivial bug fixesi
Test: atest BubbleExpandedViewTest
Test: manual - expand a bubble while folded, unfold
             => observe nothing crashes
Bug: 402550443
Change-Id: I4aa35c7cc29dbec052a082232636cc862d1e2608