Avoid ugly failure mode when moving content from a local repository that is not available.

Prelude.undefined error message was introduced by
bb4f31a0ee.

It seems best to filter out local repositories that cannot be accessed
from the list of remotes, rather than keeping them in and making every
thing that uses the list have to deal with remotes that may have an unknown
location.

Besides fixing the error message, this also makes unavailable local
remotes' names not be shown in various messages, including in git annex
status output.

Also, move --to an unavailable local repository now avoids some ugly
errors like "changeWorkingDirectory: does not exist".

Remote/Git.hs

@@ -42,7 +42,8 @@ remote = RemoteType {
 list :: Annex [Git.Repo]
 list = do
 	c <- fromRepo Git.config
-	mapM (tweakurl c) =<< fromRepo Git.remotes
+	rs <- mapM (tweakurl c) =<< fromRepo Git.remotes
+	catMaybes <$> mapM configread rs
 	where
 		annexurl n = "remote." ++ n ++ ".annexurl"
 		tweakurl c r = do
@@ -52,41 +53,47 @@ list = do
 				Just url -> inRepo $ \g ->
 					Git.Construct.remoteNamed n $
 						Git.Construct.fromRemoteLocation url g
+		{- It's assumed to be cheap to read the config of non-URL
+		 - remotes, so this is done each time git-annex is run
+		 - in a way that uses remotes.
+		 - Conversely, the config of an URL remote is only read
+		 - when there is no cached UUID value. -}
+		configread r = do
+			notignored <- repoNotIgnored r
+			u <- getRepoUUID r
+			r' <- case (repoCheap r, notignored, u) of
+				(_, False, _) -> return r
+				(True, _, _) -> tryGitConfigRead r
+				(False, _, NoUUID) -> tryGitConfigRead r
+				_ -> return r
+			{- A repo with a LocalUnknown location is not currently
+			 - accessible, so skip it. -}
+			if Git.repoIsLocalUnknown r'
+				then return Nothing
+				else return $ Just r'
+
+repoCheap :: Git.Repo -> Bool
+repoCheap = not . Git.repoIsUrl
 
 gen :: Git.Repo -> UUID -> Maybe RemoteConfig -> Annex Remote
-gen r u _ = do
- 	{- It's assumed to be cheap to read the config of non-URL remotes,
-	 - so this is done each time git-annex is run. Conversely,
-	 - the config of an URL remote is only read when there is no
-	 - cached UUID value. -}
-	let cheap = not $ Git.repoIsUrl r
-	notignored <- repoNotIgnored r
-	r' <- case (cheap, notignored, u) of
-		(_, False, _) -> return r
-		(True, _, _) -> tryGitConfigRead r
-		(False, _, NoUUID) -> tryGitConfigRead r
-		_ -> return r
-
-	u' <- getRepoUUID r'
-
-	let defcst = if cheap then cheapRemoteCost else expensiveRemoteCost
-	cst <- remoteCost r' defcst
-
-	return Remote {
-		uuid = u',
-		cost = cst,
-		name = Git.repoDescribe r',
-		storeKey = copyToRemote r',
-		retrieveKeyFile = copyFromRemote r',
-		retrieveKeyFileCheap = copyFromRemoteCheap r',
-		removeKey = dropKey r',
-		hasKey = inAnnex r',
-		hasKeyCheap = cheap,
-		whereisKey = Nothing,
-		config = Nothing,
-		repo = r',
-		remotetype = remote
-	}
+gen r u _ = new <$> remoteCost r defcst
+	where
+		defcst = if repoCheap r then cheapRemoteCost else expensiveRemoteCost
+		new cst = Remote {
+			uuid = u,
+			cost = cst,
+			name = Git.repoDescribe r,
+			storeKey = copyToRemote r,
+			retrieveKeyFile = copyFromRemote r,
+			retrieveKeyFileCheap = copyFromRemoteCheap r,
+			removeKey = dropKey r,
+			hasKey = inAnnex r,
+			hasKeyCheap = repoCheap r,
+			whereisKey = Nothing,
+			config = Nothing,
+			repo = r,
+			remotetype = remote
+		}
 
 {- Tries to read the config for a specified remote, updates state, and
  - returns the updated repo. -}