AFNetworking/AFNetworking — pull request #2088 by kyungkoo (2014-05-23 04:42:48+00:00)
Title: check self.uploadProgress inside of dispatch_async

Check self.uploadPorgess is nil or not inside dispatch_async block.
If self.uploadProgress is checked outside of dispatch_async block,
thread can not guaranteed self.uploadPorgress is not nil.

Signed-off-by: Kyungkoo Kang