Merge pull request #5270 from fredj/load_error

Load erroneous image in ol.Image#load and ol.ImageTile#load

src/ol/image.js

@@ -122,10 +122,13 @@ ol.Image.prototype.handleImageLoad_ = function() {
 
 
 /**
- * Load not yet loaded URI.
+ * Load the image or retry if loading previously failed.
+ * Loading is taken care of by the tile queue, and calling this method is
+ * only needed for preloading or for reloading in case of an error.
+ * @api
  */
 ol.Image.prototype.load = function() {
-  if (this.state == ol.ImageState.IDLE) {
+  if (this.state == ol.ImageState.IDLE || this.state == ol.ImageState.ERROR) {
     this.state = ol.ImageState.LOADING;
     this.changed();
     goog.asserts.assert(!this.imageListenerKeys_,