#1909: Crash on multiple concurrent downloads when accessing self.URLOperations dictionary.
#1909: Crash on multiple concurrent downloads when accessing self.URLOperations dictionary.

rs/SDWebImage,awkward/SDWebImage,Insfgg99x/SDWebImage,dreampiggy/SDWebImage,awkward/SDWebImage,dreampiggy/SDWebImage,dpettigrew/SDWebImage,Kekanto/SDWebImage,smule/SDWebImage,altrooz/SDWebImage,tualatrix/SDWebImage,awkward/SDWebImage,iheartradio/SDWebImage,odyth/SDWebImage,zhang-yawei/SDWebImage,dreampiggy/SDWebImage