Do not mark URLs a fail when error is due to missing network connection

SDWebImage/SDWebImageManager.m

@@ -105,9 +105,12 @@
                 completedBlock(downloadedImage, error, SDImageCacheTypeNone, finished);
 
                 if (error)
+                {
+                    if (error.code != NSURLErrorNotConnectedToInternet)
                     {
                         [self.failedURLs addObject:url];
                     }
+                }
                 else if (downloadedImage && finished)
                 {
                     [self.imageCache storeImage:downloadedImage imageData:data forKey:key toDisk:YES];