Fix listing id of empty zet

zet.dpi.c

@@ -228,13 +228,14 @@ static char *zet_get_title(const char *id, char *buf, size_t len) {
 	if (sz < 0 || (size_t)sz >= sizeof(path_buf)) return NULL;
 	int fd = open(path_buf, O_RDONLY);
 	if (fd < 0) return NULL;
-	buf = zet_get_title_fd(fd, buf, len);
+	char *title_buf = zet_get_title_fd(fd, buf, len);
-	if (buf != NULL && *buf == '\0') {
+	if (title_buf == NULL || *title_buf == '\0') {
 		strncpy(buf, "§", sigil_size);
 		strncpy(buf + sigil_size, id, len);
+		title_buf = buf;
 	}
 	close(fd);
-	return buf;
+	return title_buf;
 }
 
 static int zet_stat(const char *id, struct stat *st) {