CSV importer unable to map user when comment column has author's email

Issue Summary

The CSV importer is unable to map the user's to the comment when the email of the user is provided in the comment column of the CSV file.  

Steps to Reproduce

1. Create a new CSV file with the comment field containing the email of the author
2. Import the file in the Jira Cloud

Expected Results

The importer maps the email of the user to the required user in the site.

Actual Results

The importer is unable to find the user and maps the comment to the logged-in user instead.

Workaround

Use the username or the Atlassian account id of the user to map the author of the comment.