Pass layer to forEachFeatureAtPixel callback

This fixes a bug where the layer renderer instead of the layer is passed to the forEachFeatureAtPixel callback.

src/ol/renderer/webgl/webglimagelayerrenderer.js

@@ -89,7 +89,7 @@ ol.renderer.webgl.ImageLayer.prototype.forEachFeatureAtPixel =
        * @return {?} Callback result.
        */
       function(feature) {
-        return callback.call(thisArg, feature, this);
+        return callback.call(thisArg, feature, layer);
       });
 };