Prefer safe alternatives to getWindowAttributes

Whenever possible, prefer the safe wrappers withWindowAttributes or
safeGetWindowAttributes to getWindowAttributes.

Places where these are not applicable are limited to layouts, where
there is not good "default value" to give back in case these calls fail.
In these cases, we let the exception handling of the layout mechanism
handle it and fall back to the Full layout.

Fixes: https://github.com/xmonad/xmonad-contrib/issues/146

XMonad/Actions/UpdatePointer.hs

@@ -28,7 +28,6 @@ import XMonad
 import XMonad.Prelude
 import XMonad.StackSet (member, peek, screenDetail, current)
 
-import Control.Exception (SomeException, try)
 import Control.Arrow ((&&&), (***))
 
 -- $usage
@@ -73,10 +72,9 @@ updatePointer refPos ratio = do
   let defaultRect = screenRect $ screenDetail $ current ws
   rect <- case peek ws of
         Nothing -> return defaultRect
-        Just w  -> do tryAttributes <- io $ try $ getWindowAttributes dpy w
-                      return $ case tryAttributes of
-                        Left (_ :: SomeException) -> defaultRect
-                        Right attributes          -> windowAttributesToRectangle attributes
+        Just w  -> maybe defaultRect windowAttributesToRectangle
+               <$> safeGetWindowAttributes w
+
   root <- asks theRoot
   mouseIsMoving <- asks mouseFocused
   (_sameRoot,_,currentWindow,rootX,rootY,_,_,_) <- io $ queryPointer dpy root