Update code for invoice_prefix setting change in 5.23
Created by: seamuslee001
This updates the report code for 5.23 as per this PR https://github.com/civicrm/civicrm-core/pull/16424/files
Created by: seamuslee001
This updates the report code for 5.23 as per this PR https://github.com/civicrm/civicrm-core/pull/16424/files