When the media notification controller is requested for a session
with `getConnectedControllerForSession` and the `Future` is not null
but not yet completed, the `Future` was returned either way. This was
reported as creating a race condition between the notification
being requested for update the very first time, and the media
notification controller having completed connecting to the session.
Returning null from `getConnectedControllerForSession` when the
`Future` is available but not yet done fixes the problem. This is
safe because for the case when a notification update is dropped,
the media notification controller will trigger the update as soon
as the connection completes.
Issue: androidx/media#917
#minor-release
PiperOrigin-RevId: 595699929
5c50b27e8f