Describe the bug
When adding a new frozen author as a staff member or editor if the frozen author email is matched with an existing account and erorr occurs.

null value in column "frozen_email" of relation "submission_frozenauthor" violates not-null constraint

Janeway version
1.7.x

To Reproduce
Steps to reproduce the behavior:

1. Try to add a new frozen author where the email address matches an existing user

Expected behavior
Frozen Author record should be created.