Always execute the dismiss end runnable on silent header clear.

This fixes an edge case where the runAfter runnable was dropped, breaking the dismiss animation. On a clear animation, NSSL would use the runAfter runnable of the topmost view in the shade being animated out.  This meant that if the silent header had buggily become invisible, any clear animation which didn't affect alerting notifications (e.g. every "clear silent" animation) would result in performing the animations but NOT performing the dismiss action at the end of the animation.

With this fix, that buggy situation results in dismissing before the animation completes, which looks less than ideal, but avoids the bugged out post-dismiss state.

Fixes: 211161593
Test: manual testing making the silent view re-add
Change-Id: I378ec66ba622c521435eef2e7b032c1fed10f4ee