Move stderr of stty to pipe

If stderr is left as its default value, any error messages arising from
stty are output to the stderr of the program calling `size`, causing
strange messages if stty fails.

src/System/Console/Terminal/Windows.hs

@@ -4,6 +4,7 @@ module System.Console.Terminal.Windows(size) where
 import System.Console.Terminal.Common
 
 import Control.Monad
+import Control.Exception (evaluate)
 import Data.Word
 import Foreign.Ptr
 import Foreign.Storable
@@ -42,9 +43,12 @@ size = do
                 let stty = (shell "stty size") {
                       std_in  = UseHandle stdin
                     , std_out = CreatePipe
+                    , std_err = CreatePipe
                     }
-                (_, mbStdout, _, rStty) <- createProcess stty
+                (_, mbStdout, mbStderr, rStty) <- createProcess stty
                 exStty <- waitForProcess rStty
+                -- Drain stderr by evaluating it fully
+                maybe (pure ()) ((void . evaluate . length) <=< hGetContents) mbStderr
                 case exStty of
                     ExitFailure _ -> return Nothing
                     ExitSuccess ->