Don't render the range limit facet on zero results pages; fixes #237.

[seanaery]

• reorganize impacted existing specs so they have the data they need to render the range_facet_component

This implements @jrochkind 's idea (and annotation) described in #237 with a minor adjustment to ensure the component's predicate method render? returns a boolean true or false. It adds two new specs verifying that the facet doesn't render, and moves a few existing component specs so they continue to pass.

[jrochkind]

Hmm, while I proposed this solution -- now I'm worried about are there any cases with no min and max where we'd still want to display the form, even though we can't display the chart or facets?

I'm not sure... but maybe we'll still try this, and see how it goes?

[seanaery]

Interesting -- I can't think of any cases where we'd encounter that scenario, but I'm also not 100% certain. The way I think of it is, the facet UI element exists for three purposes: 1) narrow down the current result set, 2) show how many docs in the current result set match the currently selected value(s) for the facet, 3) remove a currently selected value w/X.

If the current result set includes no documents that have a value in the range field, then no matter what values a user would enter into the form, it won't get them any documents, so it seems safe not to render the form.

The facet itself does still render (without the chart & form) in this scenario where there's no min & max:

• User clicks [Missing] in the facet
• Result set is only documents that don't have a value in the range field
• Facet still renders, so user see they have selected [Missing], and can X that selection to remove the filter

[jrochkind]

I wonder if there's any way to actually check for non-zero results in the search results set.... accessible off that facet_item access that's all we have access to and i'm not sure what class it is!

But I think we can try this and see how it goes!