ViewModels: Delegate medialibrary callbacks

Make a delegate to remove Medialibrary callbacks management from viewmodels

vlc-android/src/org/videolan/vlc/viewmodels/CallBackDelegate.kt

@@ -35,7 +35,6 @@ interface ICallBackHandler : AbstractMedialibrary.OnMedialibraryReadyListener,
         AbstractMedialibrary.PlaylistsCb
 {
     val medialibrary : AbstractMedialibrary
-    var refreshActor : SendChannel<Unit>
 
     fun CoroutineScope.registerCallBacks(refresh: () -> Unit)
     fun releaseCallbacks()
@@ -68,7 +67,7 @@ interface ICallBackHandler : AbstractMedialibrary.OnMedialibraryReadyListener,
 class CallBackDelegate : ICallBackHandler {
 
     override val medialibrary = AbstractMedialibrary.getInstance()
-    override lateinit var refreshActor: SendChannel<Unit>
+    private lateinit var refreshActor: SendChannel<Unit>
 
     private var mediaCb = false
     private var artistsCb = false
@@ -115,6 +114,7 @@ class CallBackDelegate : ICallBackHandler {
         if (albumsCb) medialibrary.removeAlbumsCb(this)
         if (genresCb) medialibrary.removeGenreCb(this)
         if (playlistsCb) medialibrary.removePlaylistCb(this)
+        refreshActor.close()
 
     }