This change closes an edge case when an app is connecting a controller to a session that is already playing. In such a case `MediaControllerImplBase.getContentPosition()` keeps returning the first estimation for every call until `playWhenReady` changes for the first time.
Reproduction: Launch the demo-session app and start audio playback. Put the activity to the background and then to the foreground again. Go to the playlist view and `PlayerActivity` without interrupting playback and try to seek in the timebar. The position is stuck and snaps back.
PiperOrigin-RevId: 422795360
