Issue #3222637: Sign up process trying to create a user duplicate

Problem

Sign up process trying to create a user duplicate.

Solution

Ensure that a user is absent in the database before creating the user.

Issue tracker

• https://www.drupal.org/project/social_auth_extra/issues/3222637
• https://getopensocial.atlassian.net/browse/YANG-5971

How to test

• Sign up via social networks should work as before.