Reestablish completeness check for unlimited body reader

[alexbiehl]

This must have gone missing at some point.

[sol]

• rebase
• s/completeness/completion/ in commit message ("completeness check" is easily confused with other concepts)
• test case for that the cleanup action is never called more than once

[sol]

By now we have:

http-client/http-client/Network/HTTP/Client/Body.hs

Lines 108 to 119 in ed974a7

	makeUnlimitedReader
	:: IO () -- ^ cleanup
	-> Connection
	-> IO BodyReader
	makeUnlimitedReader cleanup Connection {..} = do
	icomplete <- newIORef False
	return $ do
	bs <- connectionRead
	when (S.null bs) $ do
	writeIORef icomplete True
	cleanup
	return bs

Given the cleanup action , I think this is even more crucial now.