With the change to using before_save hook to set the iid on an object,
normal validations can't be used to verify the presence of the iid.

In normal situations, the iid should always be set by either
ensure_scope_iid hook or application logic, but since we're lacking
database constraints on some tables we don't want to silently insert bad
data. To prevent unforeseen issues cause by bugs, add an additional
before_save hook to raise an exception if the iid is not set as it
should be.