jspf: add MB extension, if it does not exist

internal/backends/jspf/jspf.go

@@ -77,14 +77,11 @@ func (b *JSPFBackend) InitConfig(config *config.ServiceConfig) error {
 		Title:      config.GetString("title"),
 		Creator:    config.GetString("username"),
 		Identifier: config.GetString("identifier"),
+		Date:       time.Now(),
 		Tracks:     make([]jspf.Track, 0),
-		Extension: jspf.ExtensionMap{
-			jspf.MusicBrainzPlaylistExtensionID: jspf.MusicBrainzPlaylistExtension{
-				LastModifiedAt: time.Now(),
-				Public:         true,
-			},
-		},
 	}
+
+	b.addMusicBrainzPlaylistExtension()
 	return nil
 }
 
@@ -327,6 +324,7 @@ func (b *JSPFBackend) readJSPF() error {
 				return err
 			}
 			b.playlist = playlist.Playlist
+			b.addMusicBrainzPlaylistExtension()
 		}
 	}
 
@@ -346,3 +344,13 @@ func (b *JSPFBackend) writeJSPF() error {
 	defer file.Close()
 	return playlist.Write(file)
 }
+
+func (b *JSPFBackend) addMusicBrainzPlaylistExtension() {
+	if b.playlist.Extension == nil {
+		b.playlist.Extension = make(jspf.ExtensionMap, 1)
+	}
+	extension := jspf.MusicBrainzPlaylistExtension{Public: true}
+	b.playlist.Extension.Get(jspf.MusicBrainzPlaylistExtensionID, &extension)
+	extension.LastModifiedAt = time.Now()
+	b.playlist.Extension[jspf.MusicBrainzPlaylistExtensionID] = extension
+}