transition.end() never resolves if 0 elements are matched

[chahu]

The subject says it all. I was debugging some more complex d3 code and this behavior turned out to be the culprit. Here's a stripped down example.

https://codepen.io/chahu/pen/KKdomVZ

[Fil]

In that case no schedule has been set on any node, there is nothing to end. We should probably resolve immediately (as in #108), but it might not the behavior you would expect if you'd set a fixed duration.

[chahu]

Thanks for looking into this. Based on #108, resolving immediately seems more consistent, but either behavior is reasonable in my eyes.