[ASNetworkImageNode] Check that data is not nil before loading the animated image. (#1849)

Author: flovouin

AsyncDisplayKit/ASNetworkImageNode.mm

@@ -479,10 +479,12 @@ - (void)_lazilyLoadImageIfNecessary
             id<ASAnimatedImageProtocol> animatedImage = nil;
             if (_downloaderFlags.downloaderImplementsAnimatedImage) {
               NSData *data = [NSData dataWithContentsOfURL:_URL];
-              animatedImage = [_downloader animatedImageWithData:data];
+              if (data != nil) {
+                animatedImage = [_downloader animatedImageWithData:data];
 
-              if ([animatedImage respondsToSelector:@selector(isDataSupported:)] && [animatedImage isDataSupported:data] == NO) {
-                animatedImage = nil;
+                if ([animatedImage respondsToSelector:@selector(isDataSupported:)] && [animatedImage isDataSupported:data] == NO) {
+                  animatedImage = nil;
+                }
               }
             }