This change is in line with a recent change in how the play/pause button behaves in the player ui: if the buffering indicator is shown, it's still possible to toggle play/pause, to allow e.g. pausing videos before they even start.
This change was needed because on Android 13+ notification actions can't be null, and thus the buffering hourglass action wasn't shown.
This behavior was present before 0.24.0 and the player UI separation and
avoided crashes for which their exception contained
"Context.startForegroundService() did not then call Service.startForeground()".
Some player nullability checks have been also added, and the player service is
now stopped when it has been started from a media button and there is nothing
to play.