Commit 964b3f2 fixed an issue where dbObject was returning casting helpers for
fields that were not actually DB objects, but had something in $casting config.
However, because dbObject was no longer calling DataObject->castingHelper, this
exposed a bug that the underlying function db($fieldName) was not returning
field specs for the base fields that are created by SS automatically on all
DataObjects (i.e. Created, LastEdited, etc).
This commit fixes the underlying issue that DataObject->db($fieldName) should
return the field specs for *all* DB fields like its documentation says it will,
including those base fields that are automatically created and do not appear in
$db.
50e9eee2e9