Existing paragraph admin titles are gone after running db update to make admin title field revisionable

Problem/Motivation

After updating to version 3.1.3 and running the database update to make the admin title field revisionable, all the previously existing values for admin title are gone.

Steps to reproduce

1. on a fresh Drupal site, install Paragraph blocks 3.1.2
2. create a paragraph type and add it to a content type
3. create content add a paragraph with an admin title
4. upgrade to Paragraph blocks 3.1.3 and run the database update
5. verify the admin title in the paragraph you just created is gone

Proposed resolution

Retain existing Admin title values.