ResourceURL is omitted when a *resource.WebPage is Unmarshalled

[efixler]

This happens because we mask this field (*net.URL) in order to make it present as a string in JSON., and because we store this as a column in the db, so we don't need (or want) it in the stored JSON blob.

Hydrators are handling this manually, but it's a niggle when hydrating JSON directly, which we only do for tests.