MDEV-13560 Copy all innodb undo tablespaces from the backup directory to destination.

Do not check or rely on innodb_undo_tablespaces in copy-back,
there is no good reason for that.

extra/mariabackup/backup_copy.cc

@@ -1700,16 +1700,19 @@ copy_back()
 	ut_crc32_init();
 
 	/* copy undo tablespaces */
-	if (srv_undo_tablespaces > 0) {
+
 
 	dst_dir = (srv_undo_dir && *srv_undo_dir)
 			? srv_undo_dir : mysql_data_home;
 
 	ds_data = ds_create(dst_dir, DS_TYPE_LOCAL);
 
-		for (i = 1; i <= srv_undo_tablespaces; i++) {
+	for (i = 1; ; i++) {
 		char filename[20];
 		sprintf(filename, "undo%03u", (uint)i);
+		if (!file_exists(filename)) {
+			break;
+		}
 		if (!(ret = copy_or_move_file(filename, filename,
 														dst_dir, 1))) {
 			goto cleanup;
@@ -1718,7 +1721,6 @@ copy_back()
 
 	ds_destroy(ds_data);
 	ds_data = NULL;
-	}
 
 	/* copy redo logs */
 
@@ -1844,7 +1846,7 @@ copy_back()
 		}
 	}
 
-	/* copy buufer pool dump */
+	/* copy buffer pool dump */
 
 	if (innobase_buffer_pool_filename) {
 		const char *src_name;