#422: editing a badge no longer unchecks can_spam checkbox

Kind of a dumb error; by saying ``edit_id is None`` it always defaulted to ``True`` when creating and always defaulted the ``False`` when editing.  But that's not actually what we want; we actually want it to default to ``True`` on creating but then not apply any kind of default/change when editing so that it has whatever the last value is.

Derp.