Merge pull request #2373 from zhongwuzw/fix-loder-manager

Fix SDImageLoaderManager that only load image when loader can handle url

SDWebImage/SDImageLoadersManager.m

@@ -88,7 +88,7 @@
     NSArray<id<SDImageLoader>> *loaders = self.loaders;
     UNLOCK(self.loadersLock);
     for (id<SDImageLoader> loader in loaders.reverseObjectEnumerator) {
-        if ([loader respondsToSelector:@selector(loadImageWithURL:options:context:progress:completed:)]) {
+        if ([loader canLoadWithURL:url]) {
             return [loader loadImageWithURL:url options:options context:context progress:progressBlock completed:completedBlock];
         }
     }

SDWebImage/SDWebImagePrefetcher.h

@@ -14,7 +14,7 @@
 @interface SDWebImagePrefetchToken : NSObject <SDWebImageOperation>
 
 /**
- * Cancel the current prefeching.
+ * Cancel the current prefetching.
  */
 - (void)cancel;