Adjusted completion logic in prefetcher, as the old implementation would finish …

…prematurely if any requests were skipped.

Also adjusted documentation in headers to make it clear that the `finishedCount` includes both successful and unsuccessful requests.

@@ -20,15 +20,15 @@
  *
  * @param imagePrefetcher The current image prefetcher
  * @param imageURL The image url that was prefetched
- * @param finishedCount The total number of images that were prefetched
- * @param totalCount The total number of images that need to be prefetched
+ * @param finishedCount The total number of images that were prefetched (successful or not)
+ * @param totalCount The total number of images that were to be prefetched
  */
 - (void)imagePrefetcher:(SDWebImagePrefetcher *)imagePrefetcher didPrefetchURL:(NSURL *)imageURL finishedCount:(NSUInteger)finishedCount totalCount:(NSUInteger)totalCount;
 
 /**
  * Called when all images are prefetched.
  * @param imagePrefetcher The current image prefetcher
- * @param totalCount The total number of images that need to be prefetched
+ * @param totalCount The total number of images that were prefetched (whether successful or not)
  * @param skippedCount The total number of images that were skipped
  */
 - (void)imagePrefetcher:(SDWebImagePrefetcher *)imagePrefetcher didFinishWithTotalCount:(NSUInteger)totalCount skippedCount:(NSUInteger)skippedCount;
@@ -73,7 +73,7 @@
  * and skips images for failed downloads and proceed to the next image in the list
  *
  * @param urls list of URLs to prefetch
- * @param progressBlock block to be called when progress updates
+ * @param progressBlock block to be called when progress updates; first parameter is the number of completed (successful or not) requests, second parameter is the total number of images originally requested to be prefetched
  * @param completionBlock block to be called when prefetching is completed
  */
 - (void)prefetchURLs:(NSArray *)urls progress:(void (^)(NSUInteger, NSUInteger))progressBlock completed:(void (^)(NSUInteger, NSUInteger))completionBlock;

@@ -88,7 +88,7 @@
                 [self startPrefetchingAtIndex:self.requestedCount];
             });
         }
-        else if (self.finishedCount + self.skippedCount == self.requestedCount) {
+        else if (self.finishedCount == self.requestedCount) {
             [self reportStatus];
             if (self.completionBlock) {
                 self.completionBlock(self.finishedCount, self.skippedCount);