optimisation: avoid stat call

This commit was sponsored by Paul Walmsley on Patreon.

Command/ReKey.hs

@@ -85,7 +85,7 @@ linkKey file oldkey newkey = ifM (isJust <$> isAnnexLink file)
 	 - and vulnerable to corruption. -}
 	( getViaTmpFromDisk RetrievalAllKeysSecure DefaultVerify newkey $ \tmp -> unVerified $ do
 		oldobj <- calcRepo (gitAnnexLocation oldkey)
-		linkOrCopy' (return True) newkey oldobj tmp Nothing
+		isJust <$> linkOrCopy' (return True) newkey oldobj tmp Nothing
 	, do
 		ic <- withTSDelta (liftIO . genInodeCache file)
 	 	{- The file being rekeyed is itself an unlocked file, so if