Fix Windows build misusing 'windowsThreadBlockHack'
Fix Windows build misusing 'windowsThreadBlockHack'

windowsThreadBlockHack :: IO a -> IO a, so we want to apply it to the IO
action rather than putting it inside the 'fmap' function.

Fixes #438

rgrinberg/wai,soenkehahn/wai,dylex/wai,sordina/wai,erikd/wai,yesodweb/wai,sordina/wai,coypoop/wai,dylex/wai,frontrowed/wai,coypoop/wai,awpr/wai,rgrinberg/wai,urbanslug/wai,utdemir/wai,yesodweb/wai,rgrinberg/wai,erikd/wai,urbanslug/wai,awpr/wai,tolysz/wai,kazu-yamamoto/wai,sordina/wai,utdemir/wai,frontrowed/wai,urbanslug/wai,creichert/wai,sordina/wai,frontrowed/wai,kazu-yamamoto/wai,tolysz/wai,coypoop/wai,awpr/wai,coypoop/wai,soenkehahn/wai,tolysz/wai,dylex/wai,dylex/wai,utdemir/wai,tolysz/wai,soenkehahn/wai,erikd/wai,utdemir/wai,awpr/wai,erikd/wai,frontrowed/wai,soenkehahn/wai,creichert/wai,rgrinberg/wai,rgrinberg/wai,urbanslug/wai