Don't tc-copy missing tiles?

I have used `tc-copy` to import a local set of tile files (from `http://localhost/%(z)d/...`) into a mbtiles file.

To my surprise missing tiles (http status 404) got imported into the mbtiles file, with the HTML 404 page content. I had to manually purge these by doing `"delete from tiles where tile_data like '<!DOCTYPE%';"`