title: Access to Image from origin 'null' has been blocked by CORS policy
body: <p>I have JavaScript application in OpenLayers 3, and my base layer is created from local tiles. I work only in my computer so I do not know why I have CORS error.</p>
  
  <pre><code>    var newLayer = new ol.layer.Tile({
      source: new ol.source.OSM({
          url: 'E:/Maperitive/Tiles/vychod/{z}/{x}/{y}.png'
      })
  });
  var schladming = [21.6187, 48.7327]; // longitude first, then latitude
  // since we are using OSM, we have to transform the coordinates...
  var schladmingWebMercator = ol.proj.fromLonLat(schladming);
  
  var map = new ol.Map({
      layers: [
          newLayer
      ],
      controls: [],
      target: 'mapid',
      view: new ol.View({
          center: schladmingWebMercator,
          zoom: 10,
          minZoom: 10,
          maxZoom: 14
      })
  });
  </code></pre>
  
  <p>error message from console:</p>
  
  <blockquote>
    <p>Access to Image at <code>file:///E:/Maperitive/Tiles/vychod/10/573/352.png</code>  from origin <code>null</code> has been blocked by CORS policy: Invalid response. Origin <code>null</code> is therefore not allowed access.</p>
  </blockquote>
  
  <p>When I double-click on image URL, image is opened. Any ideas what is wrong? I never had that error before.</p>