[0.85] fix date management


git-svn-id: https://forge.indepnet.net/svn/glpi/branches/0.85-work@20661 35612d4c-9d10-0410-837c-bf9dd1be60d7
[0.85] check also validity date - fixed #4227

git-svn-id: https://forge.indepnet.net/svn/glpi/branches/0.85-work@20662 35612d4c-9d10-0410-837c-bf9dd1be60d7