Fix crash when sorting albums with a null artist

Reviewed-on: #1

app/src/main/java/com/cappielloantonio/tempo/ui/adapter/AlbumCatalogueAdapter.java

@@ -157,7 +157,7 @@ public class AlbumCatalogueAdapter extends RecyclerView.Adapter<AlbumCatalogueAd
                 albums.sort(Comparator.comparing(AlbumID3::getName));
                 break;
             case Constants.ALBUM_ORDER_BY_ARTIST:
-                albums.sort(Comparator.comparing(AlbumID3::getArtist));
+                albums.sort(Comparator.comparing(AlbumID3::getArtist, Comparator.nullsLast(Comparator.naturalOrder())));
                 break;
             case Constants.ALBUM_ORDER_BY_YEAR:
                 albums.sort(Comparator.comparing(AlbumID3::getYear));

app/src/main/java/com/cappielloantonio/tempo/ui/dialog/PlaylistChooserDialog.java

@@ -101,7 +101,7 @@ public class PlaylistChooserDialog extends DialogFragment implements ClickCallba
         Playlist playlist = bundle.getParcelable(Constants.PLAYLIST_OBJECT);
 
         playlistChooserViewModel.isSongInPlaylist(Objects.requireNonNull(playlist).getId(), requireActivity()).observe(requireActivity(), songInPlaylist -> {
-            if (songInPlaylist) {
+            if (!songInPlaylist) {
                 playlistChooserViewModel.addSongToPlaylist(playlist.getId());
                 dismiss();
             } else {