also avoid crashing in most circumstances if unable to determine the username

Mostly the username is only used for the git committer or other display
purposes, and we can just fall back to a dummy value in these cases.

The only remaining place where an error is thrown is when starting local
pairing, which needs the username to be known.

Annex/Init.hs

@@ -52,13 +52,11 @@ genDescription (Just d) = return d
 genDescription Nothing = do
 	reldir <- liftIO . relHome =<< liftIO . absPath =<< fromRepo Git.repoPath
 	hostname <- fromMaybe "" <$> liftIO getHostname
-#ifndef mingw32_HOST_OS
 	let at = if null hostname then "" else "@"
-	username <- liftIO myUserName
-	return $ concat [username, at, hostname, ":", reldir]
-#else
-	return $ concat [hostname, ":", reldir]
-#endif
+	v <- liftIO myUserName
+	return $ concat $ case v of
+		Right username -> [username, at, hostname, ":", reldir]
+		Left _ -> [hostname, ":", reldir]
 
 initialize :: Maybe String -> Maybe Version -> Annex ()
 initialize mdescription mversion = do