AudioModels: Set correct sorting criteria

SharedSources/MediaLibraryModel/AlbumModel.swift

@@ -106,7 +106,7 @@ extension AlbumModel: MediaLibraryObserver {
 
 extension VLCMLAlbum: MediaCollectionModel {
     func sortModel() -> SortModel? {
-        return nil
+        return SortModel([.alpha, .album, .duration, .releaseDate])
     }
 
     func files(with criteria: VLCMLSortingCriteria,

SharedSources/MediaLibraryModel/ArtistModel.swift

@@ -91,7 +91,7 @@ extension ArtistModel: MediaLibraryObserver {
 extension VLCMLArtist: MediaCollectionModel {
 
     func sortModel() -> SortModel? {
-        return SortModel([.alpha])
+        return SortModel([.alpha, .album, .duration, .releaseDate])
     }
 
     func files(with criteria: VLCMLSortingCriteria,

SharedSources/MediaLibraryModel/GenreModel.swift

@@ -104,7 +104,7 @@ extension VLCMLGenre {
 
 extension VLCMLGenre: MediaCollectionModel {
     func sortModel() -> SortModel? {
-        return SortModel([.alpha])
+        return SortModel([.alpha, .album, .duration, .releaseDate])
     }
 
     func files(with criteria: VLCMLSortingCriteria,

SharedSources/MediaLibraryModel/TrackModel.swift

@@ -12,7 +12,7 @@
 class TrackModel: MediaModel {
     typealias MLType = VLCMLMedia
 
-    var sortModel = SortModel([.alpha, .duration, .fileSize])
+    var sortModel = SortModel([.alpha, .album, .duration, .fileSize])
 
     var updateView: (() -> Void)?