Ensure "done" callback is invoked if zero-length paths array is provided

[revetkn]

It is uncommon but possible for script.js to be invoked with [] paths. Current behavior is to never fire the "done" callback, this fix ensures it's called immediately and skips the setTimeout.

Github's diff is a bit misleading - it shows mostly whitespace. I've only added a one-line if statement.

[ded]

interesting, i'll have a stab at getting this in one way or another