title: Mapbox: Update custom layer paint property
body: <p>Working on a mapbox project. I have created a custom layer, and am looking to update a paint property of that layer. Methods I've tried don't work. Here are the details:</p>
  
  <p>The layer I create:</p>
  
  <pre><code>map.addLayer({
          id: 'points-circle',
          source: 'points',
          type: 'circle',
          paint: {
            'circle-radius': pointSize*.6,
            'circle-color': {type: 'identity', property: 'color'},
          }
        })
  </code></pre>
  
  <p>Later, I try to update the <code>circle-radius</code> property, like so:</p>
  
  <pre><code>map.setPaintProperty('points-circle','circle-radius', pointSize*.6)
  </code></pre>
  
  <p>This fails with the error: <code>Error: The layer 'points-circle' does not exist in the map's style and cannot be styled.</code> How do I update my circle-radius of my custom added layer?</p>