better interface for catKey'

It only needs the size, so don't require the other stuff. Should let it
be used in more places, making things faster.

Annex/CatFile.hs

@@ -133,10 +133,12 @@ catFileStop = do
 
 {- From ref to a symlink or a pointer file, get the key. -}
 catKey :: Ref -> Annex (Maybe Key)
-catKey ref = catKey' ref =<< catObjectMetaData ref
+catKey ref = catObjectMetaData ref >>= \case
+	Just (_, sz, _) -> catKey' ref sz
+	Nothing -> return Nothing
 
-catKey' :: Ref -> Maybe (Sha, Integer, ObjectType) -> Annex (Maybe Key)
-catKey' ref (Just (_, sz, _))
+catKey' :: Ref -> FileSize -> Annex (Maybe Key)
+catKey' ref sz
 	-- Avoid catting large files, that cannot be symlinks or
 	-- pointer files, which would require buffering their
 	-- content in memory, as well as a lot of IO.

Command/Smudge.hs

@@ -105,7 +105,10 @@ clean file = do
 		Nothing -> do
 			let fileref = Git.Ref.fileRef file
 			indexmeta <- catObjectMetaData fileref
-			go' b indexmeta =<< catKey' fileref indexmeta
+			oldkey <- case indexmeta of
+				Just (_, sz, _) -> catKey' fileref sz
+				Nothing -> return Nothing
+			go' b indexmeta oldkey
 	go' b indexmeta oldkey = ifM (shouldAnnex file indexmeta oldkey)
 		( do
 			-- Before git 2.5, failing to consume all stdin here