fix validate users list of a change

git-svn-id: https://forge.indepnet.net/svn/glpi/trunk@23257 35612d4c-9d10-0410-837c-bf9dd1be60d7
fix change cost - fixed #5145

git-svn-id: https://forge.indepnet.net/svn/glpi/trunk@23258 35612d4c-9d10-0410-837c-bf9dd1be60d7