Please cache only successful embeds

[Toutouwai]

By default the module caches the embed code for each video, but it would be good if it only cached successful embeds. My client had an issue where they attempted to embed a non-public Vimeo video and on the frontend it showed an error like "https://vimeo.com/123456 (404)". That's expected, but when they fixed this by making the video public the frontend continued to show the error and it took me a while to work out that I needed to visit the module settings page and clear the cache.