Duplicated users displayed as suggestion

Summary

When adding a user to the Request Participant field, duplicated users are suggested if you have the same user on multiple directories

Steps to Reproduce

1. Have 2 directories with the same user
2. Start typing the name of this user in the Request Participants field

Expected Results

JIRA suggests the user once as it is done in any other User field

Actual Results

JIRA displays the user multiple times as a suggestion

Notes

• This can be reproduced either in the Customer Portal request via the "Add People" button or through the JIRA view screen in the Request Participants field
• Same issue happen for Reporter field but not Assignee field. Does not seem to affect JIRA Service Desk specifically.