Update role_mappings to avoid data loss

Does this update help auto-mapping new openID users to existing user's roles?

Just tested out the overnight dev version. confirm that it works

FWIW: As a work-around for those seeing permissions disappearing, adding a role mapping in the openid_connect/settings page, saving, and then removing it and saving again updates the settings to remove all empty values (as the patch does) and avoids the problem.