Fix crash when DISPLAY_CONTENT while playing

[3l0w]

When a video is playing and on another device you browse libraries on a casting device it cause the app to crash.
The onDisplayContent method is trying to read ExoPlayer state but from the socket thread and not the main thread.

java.lang.IllegalStateException: Player is accessed on the wrong thread. Current thread: 'DefaultDispatcher-worker-4'
Expected thread: 'main'
See https://developer.android.com/guide/topics/media/issues/player-accessed-on-wrong-thread
	at androidx.media3.exoplayer.ExoPlayerImpl.verifyApplicationThread(ExoPlayerImpl.java:2842)
	at androidx.media3.exoplayer.ExoPlayerImpl.getPlaybackState(ExoPlayerImpl.java:514)
	at androidx.media3.common.BasePlayer.isPlaying(BasePlayer.java:124)
	at org.jellyfin.androidtv.ui.playback.VideoManager.isPlaying(VideoManager.java:341)
	at org.jellyfin.androidtv.ui.playback.PlaybackController.isPlaying(PlaybackController.java:262)
	at org.jellyfin.androidtv.data.eventhandling.SocketHandler.onDisplayContent(SocketHandler.kt:184)
	at org.jellyfin.androidtv.data.eventhandling.SocketHandler.lambda$13$lambda$8(SocketHandler.kt:103)
	at org.jellyfin.androidtv.data.eventhandling.SocketHandler$$ExternalSyntheticLambda3.onReceive(Unknown Source:4)
	at org.jellyfin.androidtv.data.eventhandling.SocketHandler$_init_$lambda$13$$inlined$addGeneralCommandsListener$default$1.onReceive(ListenerRegistrationExtensions.kt:68)
	at org.jellyfin.sdk.api.sockets.helper.ListenerHelper.forwardMessage(ListenerHelper.kt:37)
	at org.jellyfin.sdk.api.sockets.SocketInstance.forwardMessage(SocketInstance.kt:283)
	at org.jellyfin.sdk.api.sockets.SocketInstance.access$forwardMessage(SocketInstance.kt:35)
	at org.jellyfin.sdk.api.sockets.SocketInstance$connectAndBind$2.invokeSuspend(SocketInstance.kt:220)
	at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
	at kotlinx.coroutines.DispatchedTask.run(DispatchedTask.kt:108)
	at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:584)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.executeTask(CoroutineScheduler.kt:793)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.runWorker(CoroutineScheduler.kt:697)
	at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:684)

Changes
Forced the method onDisplayContent to run on the main thread.

[nielsvanvelzen]

Thanks!