some filters flatten country highlighting

[mrjones-plip]

on some filters the country's colors all become the same instead of having the correct, discrete values.

steps to reproduce:

1. go to PCH's IXP Dir: https:/pch.net/ixp
2. add a filter "PCH Present: Yes"

expected: countries colors remain accurate based on defined map.countries.attr.fill.transform() and values of remaining countries after the filter
actual: countries all become the same gray color
note 1: choosing "No" seems to work as expected
note 2: if this is a bug in PCH's implementation - please call us out, we don't want to bother y'all if it's endemic to our site!

[mrjones-plip]

Here's before:

And here's after: