Memory leak when trying to render a subworkflow

If you use `cwl-svg` to render a CWL workflow, and then use `workflow.draw()` on another workflow that was originally inside the original workflow, the page will get stuck in an infinite loop and in my case, crash your browser.

To demonstrate, the simplest case I can recreate is here: https://github.com/TMiguelT/CwlSvgBug (instructions included)