Fullname and Emailaddress functions are not working when the username is modified.

Steps to reproduce:

• Create a new user (username: xporteruser123)
• Create a new issue and assign it to this new user
• Create a template to print: ${AssigneeId}, ${fullname:AssigneeId}, ${emailaddress:AssigneeId}
• Export the issue and verify if it's working as expected.

• Change the username to xporteruser
• Try to export the issue again.