MediaCollectionModel: Set default sort criteria to default

SharedSources/MediaLibraryModel/AlbumModel.swift

@@ -109,7 +109,7 @@ extension VLCMLAlbum: MediaCollectionModel {
         return nil
     }
 
-    func files(with criteria: VLCMLSortingCriteria = .alpha,
+    func files(with criteria: VLCMLSortingCriteria,
                desc: Bool = false) -> [VLCMLMedia]? {
         return tracks(with: criteria, desc: desc)
     }

SharedSources/MediaLibraryModel/ArtistModel.swift

@@ -94,7 +94,7 @@ extension VLCMLArtist: MediaCollectionModel {
         return SortModel([.alpha])
     }
 
-    func files(with criteria: VLCMLSortingCriteria = .alpha,
+    func files(with criteria: VLCMLSortingCriteria,
                desc: Bool = false) -> [VLCMLMedia]? {
         return tracks(with: criteria, desc: desc)
     }

SharedSources/MediaLibraryModel/GenreModel.swift

@@ -107,7 +107,7 @@ extension VLCMLGenre: MediaCollectionModel {
         return SortModel([.alpha])
     }
 
-    func files(with criteria: VLCMLSortingCriteria = .alpha,
+    func files(with criteria: VLCMLSortingCriteria,
                desc: Bool = false) -> [VLCMLMedia]? {
         return tracks(with: criteria, desc: desc)
     }

SharedSources/MediaLibraryModel/MediaLibraryBaseModel.swift

@@ -113,7 +113,7 @@ extension VLCMLObject {
 }
 
 extension MediaCollectionModel {
-    func files(with criteria: VLCMLSortingCriteria = .alpha,
+    func files(with criteria: VLCMLSortingCriteria = .default,
                desc: Bool = false) -> [VLCMLMedia]? {
         return files(with: criteria, desc: desc)
     }