User within organization cannot Share issue with themselves

Issue Summary

This is reproducible on Data Center: (yes)

When a user that is within an organization tries to Share an issue with themself, an error pops up saying that they does not belong to the organization.

Steps to Reproduce

1. Create a Service Desk project
2. Create an organization
3. Add User 1 and User 2 to it
4. Create an issue as User 1
5. Login as User 2, access the create request and attempt to add yourself through the Share option

Expected Results

The request would be shared with the user account that was entered on the request portal when "sharing" the request.

Actual Results

An error saying that the user does not belong to the Organization will pop up. However, users are able to share the same request with other customers from the same organization.

Workarounds

1. Click on the "Get notifications" link to subscribe to the notifications as org member
2. Have an agent manually add the user through JIRA's request participant feature on the issue in the Jira UI
3. Adjust the "customer permissions" so that "Who can customers share requests with?" is set to "Any customer, by typing an email address"