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.

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