The standard mail action does not allow attachments. You need to create a derivative. There is one on the internet which I downloaded and it works fine with 4.2c but I really can't remember where I got it from.
Happy to share it with your but I can't attach it to this post so send me a message with an email address & I will forward it on.
Alternatively, Google for "alfresco mail with attachments action" and you should find it.
That said, this allows you to attach an Alfresco document, so you would have to create the XML document in Javascript, save it to the reporsitory and then you could attach it. Thats easy enough to do with a couple of extra lines of code in your example above.