If a data field starts with no value (this happens when a supertag repeater is added), assign the value as an empty array.
Accounted for dynamically added supertag fields

Previously, we were looping through all supertag fields and
initializing them on page load. This caused supertag fields that
were added to the page after the initial page load (like on a
repeater field) to not be initialized. To fix this problem, I
hooked in to the "acf/setup_fields" trigger. When this trigger is
called, we find all supertag fields and initialize them.