add: avoid ugly error message when adding a deleted file in direct mode

Due to add using withFilesMaybeModified, it will get files that have been
deleted but are still in the index. So catch the IO error that results when
trying to stat such a file.

Command/Add.hs

@@ -56,12 +56,14 @@ start :: FilePath -> CommandStart
 start file = ifAnnexed file addpresent add
   where
 	add = do
-		s <- liftIO $ getSymbolicLinkStatus file
-		if isSymbolicLink s || not (isRegularFile s)
-			then stop
-			else do
-				showStart "add" file
-				next $ perform file
+		ms <- liftIO $ catchMaybeIO $ getSymbolicLinkStatus file
+		case ms of
+			Nothing -> stop
+			Just s
+				| isSymbolicLink s || not (isRegularFile s) -> stop
+				| otherwise -> do
+					showStart "add" file
+					next $ perform file
 	addpresent (key, _) = ifM isDirect
 		( ifM (goodContent key file) ( stop , add )
 		, fixup key