What if a layer has no features? Or an attribute more values?

[davidtheclark]

We need to make sure these cases are covered.

[mapsam]

@davidtheclark currently if you pass a geojson with no features, the output looks like this:

{
  layerCount: 1,
  layers: [
    {
      attributeCount: 0,
      attributes: [],
      count: 0,
      layer: 'no-features'
    }
  ]
}

Is this acceptable?

[davidtheclark]

@mapbox-machine: Seems fine to me!