Always parse radio facets as Arrays

In order to link back to the pre filtered Finders, we need to have a started way of linking backing to select and radio facets. To do this, we turn the radio facet values into an array and take the first value when we check it against the allowed_values. This also means we should remove the test which was safeguarding against this.
This line feels a little hard to read. Is it worth using one or two variables to clarify what it is doing.