fix undefined property usage

[Athorcis]

reports_cleaner scripts was failing with the following error

dmarc-srg [error]: ErrorException: Undefined property: Liuch\DmarcSrg\Database\Mariadb\ReportMapper::$user in /var/www/dmarc-srg/classes/Database/Mariadb/ReportMapper.php:397
Stack trace:
#0 /var/www/dmarc-srg/classes/Database/Mariadb/ReportMapper.php(397): {closure}(2, 'Undefined prope...', '/var/www/dmarc-...', 397)
#1 /var/www/dmarc-srg/classes/Report/ReportList.php(187): Liuch\DmarcSrg\Database\Mariadb\ReportMapper->delete(Array, Array, Array)
#2 /var/www/dmarc-srg/utils/reports_cleaner.php(78): Liuch\DmarcSrg\Report\ReportList->delete()
#3 {main}
Error: Undefined property: Liuch\DmarcSrg\Database\Mariadb\ReportMapper::$user (-1)

[liuch]

Thank you very much.