Make vector-layer example ignore XHR errors

This is a workaround for our check-example.js PhantomJS script to work with this example. Without this check-example.js fails because xhr.status is 0. I tried to give the explicit file:/// scheme as indicated in https://groups.google.com/d/msg/phantomjs/wFGme0pE-Tk/WUjU5s-27NwJ, but that didn't work for me.

examples/vector-layer.js

@@ -51,8 +51,6 @@ xhr.onload = function() {
     // this is silly to have to tell the layer the destination projection
     var projection = map.getView().getProjection();
     vector.parseFeatures(xhr.responseText, geojson, projection);
-  } else {
-    throw new Error('Data loading failed: ' + xhr.status);
   }
 };
 xhr.send();