Add error handler to ASNetworkImageNodeDelegate

AsyncDisplayKit/ASNetworkImageNode.h

@@ -95,6 +95,16 @@ NS_ASSUME_NONNULL_BEGIN
 
 @optional
 
+/**
+ * Notification that the image node failed to download the image.
+ *
+ * @param imageNode The sender.
+ * @param error The error with details.
+ *
+ * @discussion Called on a background queue.
+ */
+- (void)imageNode:(ASNetworkImageNode *)imageNode didFailWithError:(NSError *)error;
+
 /**
  * Notification that the image node finished decoding an image.
  *