playlist_song: allow references to songs outside the musicdir

When we have an absolute path that's not inside the music directory,
allow loading it anyway, if we're in "secure" mode (i.e. the client is
connected via UNIX socket).

src/playlist_song.c

@@ -140,6 +140,12 @@ playlist_check_translate_song(struct song *song, const char *base_uri,
 	if (uri_has_scheme(uri)) {
 		dest = song_remote_new(uri);
 		g_free(uri);
+	} else if (g_path_is_absolute(uri) && secure) {
+		dest = song_file_load(uri, NULL);
+		if (dest == NULL) {
+			song_free(song);
+			return NULL;
+		}
 	} else {
 		dest = db_get_song(uri);
 		g_free(uri);