converted reads from stderr to use hGetLineUntilExitOrEOF

These are all unlikely to suffer from the inherited stderr fd problem,
but who knows, it could happen.

Annex/YoutubeDl.hs

@@ -225,16 +225,19 @@ youtubeDlFileNameHtmlOnly' url uo
 		liftIO $ withCreateProcess p waitproc
 	
 	waitproc Nothing (Just o) (Just e) pid = do
-		output <- fmap fst $ 
-			hGetContentsStrict o
-				`concurrently`
-			hGetContentsStrict e
+		errt <- async $ discardstderr pid e
+		output <- hGetContentsStrict o
 		ok <- liftIO $ checkSuccessProcess pid
+		wait errt
 		return $ case (ok, lines output) of
 			(True, (f:_)) | not (null f) -> Right f
 			_ -> nomedia
 	waitproc _ _ _ _ = error "internal"
 
+	discardstderr pid e = hGetLineUntilExitOrEOF pid e >>= \case
+		Nothing -> return ()
+		Just _ -> discardstderr pid e
+
 	nomedia = Left "no media in url"
 
 youtubeDlOpts :: [CommandParam] -> Annex [CommandParam]