MDEV-13332 mariabackup from 10.2.x crashes with --ftwrl-* options

Fixed null pointer dereference in parsing "show full processlist" output
with atoi().

Some  Innodb background thread has NULL in 'Time' column,
thus  backup would crash with when atoi is applied to null pointer.

extra/mariabackup/backup_mysql.cc

@@ -724,7 +724,7 @@ have_queries_to_wait_for(MYSQL *connection, uint threshold)
 	all_queries = (opt_lock_wait_query_type == QUERY_TYPE_ALL);
 	while ((row = mysql_fetch_row(result)) != NULL) {
 		const char	*info		= row[7];
-		int		duration	= atoi(row[5]);
+		int		duration	= row[5] ? atoi(row[5]) : 0;
 		char		*id		= row[0];
 
 		if (info != NULL
@@ -754,7 +754,7 @@ kill_long_queries(MYSQL *connection, time_t timeout)
 	all_queries = (opt_kill_long_query_type == QUERY_TYPE_ALL);
 	while ((row = mysql_fetch_row(result)) != NULL) {
 		const char	*info		= row[7];
-		long long		duration	= atoll(row[5]);
+		long long		duration	= row[5]? atoll(row[5]) : 0;
 		char		*id		= row[0];
 
 		if (info != NULL &&

mysql-test/suite/mariabackup/incremental_backup.test

@@ -14,7 +14,7 @@ exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf  --backup --target-dir
 --enable_result_log
 INSERT INTO t VALUES(2);
 SELECT * FROM t;
-exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf  --backup --target-dir=$incremental_dir --incremental-basedir=$basedir;
+exec $XTRABACKUP --defaults-file=$MYSQLTEST_VARDIR/my.cnf  --backup --ftwrl-wait-timeout=5 --ftwrl-wait-threshold=300 --ftwrl-wait-query-type=all --target-dir=$incremental_dir --incremental-basedir=$basedir;
 
 --disable_result_log
 echo # Prepare full backup, apply incremental one;