mariabackup - do not extend innodb tablespaces in prepare, unless

incremental prepare is running.

extra/mariabackup/xtrabackup.cc

@@ -6546,6 +6546,8 @@ xtrabackup_prepare_func(int argc, char ** argv)
 	if(innodb_init())
 		goto error_cleanup;
 
+	if (xtrabackup_incremental) {
+
 	it = datafiles_iter_new(fil_system);
 	if (it == NULL) {
 		msg("xtrabackup: Error: datafiles_iter_new() failed.\n");
@@ -6588,6 +6590,8 @@ xtrabackup_prepare_func(int argc, char ** argv)
 
 	datafiles_iter_free(it);
 
+	} /* if (xtrabackup_incremental) */
+
 	if (xtrabackup_export) {
 		msg("xtrabackup: export option is specified.\n");
 		os_file_t	info_file = XB_FILE_UNDEFINED;