Also listen on loading images

This fixes a bug that occured when an image source was used by multiple maps. In that case the map that didn't load the image wouldn't register a load listener on that image and would therefore not call render to request a re-render of the map.

src/ol/renderer/webgl/webglvectorlayerrenderer.js

@@ -108,7 +108,7 @@ ol.renderer.webgl.VectorLayer.prototype.forEachFeatureAtPixel =
  * @param {goog.events.Event} event Image style change event.
  * @private
  */
-ol.renderer.webgl.VectorLayer.prototype.handleImageChange_ =
+ol.renderer.webgl.VectorLayer.prototype.handleStyleImageChange_ =
     function(event) {
   this.renderIfReadyAndVisible();
 };
@@ -232,7 +232,7 @@ ol.renderer.webgl.VectorLayer.prototype.renderFeature =
     loading = ol.renderer.vector.renderFeature(
         replayGroup, feature, styles[i],
         ol.renderer.vector.getSquaredTolerance(resolution, pixelRatio),
-        this.handleImageChange_, this) || loading;
+        this.handleStyleImageChange_, this) || loading;
   }
   return loading;
 };