Unable to migrate account from email to SAML

Repro steps:
1. Configure a Mattermost server with SAML (or use an existing one)
2. Log in with an email account
3. From account settings -> security, migrate your account to SAML
4. Enter current email account's password and hit enter
5. (skipped if already signed in) Enter credentials for SAML account

Observed: Migration fails after logging into SAML provider
Expected: Migration successful

Reproduces on community, community-release, community-daily.

Candidate for hotfix.