When the AdTagLoader is deactivated because of a player error, the
error callback is already pending on the app's main thread, but not
yet executed. This means the VideoAdPlayerCallback instances
registered in AdTagLoader won't receive this error event if the
Player.Listener is immediately removed from AdTagLoader.
This can be fixed by postponing the deregistration until after
already pending messages have been handled. As this means other
callbacks can be triggered now with player==null, this check needs
to be added to other callbacks to avoid handling stale events.
Issue: androidx/media#1334
PiperOrigin-RevId: 630068222
7cf2fd9486