Fix nautilus script installation to not crash when the nautilus script dir does not exist. Instead, only install scripts when the directory already exists.

nautilus creates this directory each time run, so this avoids putting cruft
in user's home

Assistant/Install.hs

@@ -87,8 +87,9 @@ installNautilus :: FilePath -> IO ()
 #ifdef linux_HOST_OS
 installNautilus program = do
 	scriptdir <- (\d -> d </> "nautilus" </> "scripts") <$> userDataDir
-	genscript scriptdir "get"
-	genscript scriptdir "drop"
+	whenM (doesDirectoryExist scriptdir) $ do
+		genscript scriptdir "get"
+		genscript scriptdir "drop"
   where
 	genscript scriptdir action =
 		installscript (scriptdir </> scriptname action) $ unlines