Invitation email uses inviter current URL instead of the Base URL

Summary

When inviting a customer/sending an invitation email through JIRA Service Desk, the invitation uses the inviter current URL instead of using the Base URL, causing problems if the inviter is using localhost, for example.

Steps to Reproduce

1. Install latest JIRA and JIRA Service Desk;
2. Configure the Base URL in the Administration » General Configuration page to e.g. "my.jira.com";
3. Access JIRA using localhost or a different URL that is different from JIRA's Base URL.
4. Configure an outgoing mail for JIRA;
5. Create a new Service Desk;
6. Navigate to Service Desk » "My First Service Desk" » People » Customers;
7. Click Invite customers and send an invitation to an email.

Expected Results

The Visit Portal button would send the invitee to the JIRA Base URL.

Actual Results

The invitee is sent to the URL the inviter was accessing JIRA Service Desk from.

Workaround

Send invites when accessing JIRA through the Base URL.