fix(validation): validation error ExtractErrors method should not bail at missing top level fields

[mike-winberry]

Environment

App version: 0.4.2

Steps to reproduce

1. This is currently unreproducable except when used as a library
2. see feat(common): json schema linting for common validation(s) lula#473 src/pkg/common/schema/schema.go

Expected result

• get a proper error returned from validation.ExtractErrors

Actual Result

• get a json null value

Severity/Priority

• Not directly effecting the functionality of gooscal but does have a negative side effect when extending the library.