Administrator Emails Not Sent with bad From User variable

When creating a form that automatically sends an email to the Administrator when submitted, Web Forms doesn’t validate that the variables are correct in the “From Name” field.

1. If an editor enters an invalid form variable: e.g. %user%, and that field doesn’t exist, I can save that form without error. When forms are later submitted by end-users, the emails silently fail because the From part of the SMTP submission has an invalid user name: %user%
2. If an editor changes a field name after using the field name in the From Name field (see #1), it’s no longer valid, and creating new submissions will fail to send to the administrator as in #1.