login_security_track null name entries - DB error

Login Security adds validation callbacks to add a login_security_track row when a login is unsuccessful.

However, they are added before core validation but don't handle a null entry for the username, allowing login_security_track rows with an empty 'name' value.

For us, that created a DB error on successful logins, like …

Duplicate entry '' for key 'name': INSERT INTO {users} …

… presented as a 500 error to the user. Not good, really.