Change size_t value from NULL to 0 to suppress compiler warning.

Author: Darryl H. Thomas

AFNetworking/AFImageRequestOperation.m

@@ -78,7 +78,7 @@ static dispatch_queue_t image_request_operation_processing_queue() {
     size_t width = CGImageGetWidth(imageRef);
     size_t height = CGImageGetHeight(imageRef);
     size_t bitsPerComponent = CGImageGetBitsPerComponent(imageRef);
-    size_t bytesPerRow = NULL; // CGImageGetBytesPerRow() calculates incorrectly in iOS 5.0, so defer to CGBitmapContextCreate()
+    size_t bytesPerRow = 0; // CGImageGetBytesPerRow() calculates incorrectly in iOS 5.0, so defer to CGBitmapContextCreate()
     CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
     CGBitmapInfo bitmapInfo = CGImageGetBitmapInfo(imageRef);