Add an option called "SDWebImageAvoidAutoImageFill" to avoid automatic image add…

…ition in UIImageView and let developer to do it himself

@@ -82,6 +82,13 @@ typedef NS_OPTIONS(NSUInteger, SDWebImageOptions) {
      * Use this flag to transform them anyway.
      */
     SDWebImageTransformAnimatedImage = 1 << 10,
+    
+    /**
+     * By default, image is added to the imageView after download. But in some cases, we want to
+     * have the hand before setting the image (apply a filter or add it with cross-fade animation for instance)
+     * Use this flag if you want to manually set the image in the completion when success
+     */
+    SDWebImageAvoidAutoImageFill = 1 << 11
 };
 
 typedef void(^SDWebImageCompletionBlock)(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL);

@@ -54,7 +54,12 @@ static char imageURLKey;
             if (!wself) return;
             dispatch_main_sync_safe(^{
                 if (!wself) return;
-                if (image) {
+                if (image && (options & SDWebImageAvoidAutoImageFill) && completedBlock)
+                {
+                    completedBlock(image, error, cacheType, url);
+                    return;
+                }
+                else if (image) {
                     wself.image = image;
                     [wself setNeedsLayout];
                 } else {