Taxonomy reference field prints label for empty fields

Issue Summary

When using the hs_taxonomy field formatters, the field label is printed even when the field is empty. This is because of the #attached property being added to the render array. Even though the render array has no children, that property must be enough for the field label to still print.

Here's a patch that just returns early in the field formatter process if the field is empty. An upside of this is that it also saves on a couple taxonomy term/vocabulary loads if the field is empty as well.