Add overlayfinishing state.

There was an error due to unbind during an async function causing the
connection to be set to null before unbind is called.
Add overlayfinishing state to prevent overlay finishing consumer to be
added twice causing a NullPointerException.

Bug: 267335683
Test: Manually tested to see that the error can no longer be repro'd.
Change-Id: I1cfb5bd68c6568e304bb55064794aa0e09075d56