Rendering fitted end point shows periodically

[nickofthyme]

Describe the bug When using a fitting function where the data creates an orphan point. The canvas renderer will flip-flop seemingly based on width whether to render the area as filled (incorrect) or an orphan point.

To Reproduce Steps to reproduce the behavior:

1. Go to the stacked fitting function story
2. Select ordinal x dataset
3. Drag sidebar/window to change the chart width
4. Notice the area between l and m on series test will flash filled and unfilled.

https://user-images.githubusercontent.com/19007109/141022233-2ec26da9-9d22-4eed-858e-fe894234d897.mp4

Expected behaviour There should be no flickering and the orphan point should have no fill.

Good 👍🏼

Bad 👎🏼

Version (please complete the following information):

• OS: Mac
• Browser: Chrome
• Elastic Charts: latest

[nickofthyme]

Also noticed this on https://elastic.github.io/elastic-charts/?path=/story/line-chart--test-path-ordering&globals=theme:light.