UI Glitch when hiding/showing series while this plugin is enabled

[philfontaine]

The problem only occurs when this plugin is enabled. When we click on a dataset in the legend to hide it, then click again to show it while it was still animating there is a small UI glitch that happens. For a split second, the dataset is completely shown, and then it starts its animation from hidden to shown.

It's not very obvious from the GIF, but it is easy to notice when you run the code pen yourself.

https://codepen.io/philfontaine/pen/VwbMNMv

[kurkle]

This was fixed by #772