MDEV-30293: mariabackup fail with --galera-info option without Galera

Without Galera, mariabackup should ignore the --galera-info option
and not fail with rc != 0 like it does now. This commit fixes this flaw.

extra/mariabackup/backup_copy.cc

@@ -1544,8 +1544,6 @@ bool backup_start(CorruptedPages &corrupted_pages)
 		if (!write_galera_info(mysql_connection)) {
 			return(false);
 		}
-                // copied from xtrabackup. what is it needed for here?
-		write_current_binlog_file(mysql_connection);
 	}
 
 	if (opt_binlog_info == BINLOG_INFO_ON) {

extra/mariabackup/backup_mysql.cc

@@ -1558,14 +1558,18 @@ write_galera_info(MYSQL *connection)
 
 	if ((state_uuid == NULL && state_uuid55 == NULL)
 		|| (last_committed == NULL && last_committed55 == NULL)) {
-		msg("Failed to get master wsrep state from SHOW STATUS.");
-		result = false;
+		msg("Warning: failed to get master wsrep state from SHOW STATUS.");
+		result = true;
 		goto cleanup;
 	}
 
 	result = backup_file_printf(XTRABACKUP_GALERA_INFO,
 		"%s:%s\n", state_uuid ? state_uuid : state_uuid55,
 			last_committed ? last_committed : last_committed55);
+	if (result)
+	{
+		write_current_binlog_file(connection);
+	}
 
 cleanup:
 	free_mysql_variables(status);