Stacked points on area series connect line to fitted point

[nickofthyme]

Describe the issue
When using a stacked area series, setting an isolated value in the data correctly places the point but treats the next point as a real point when it is actually fitted in order to allow stacking.

To Reproduce
Steps to reproduce the behavior:

1. Go to https://codesandbox.io/s/quirky-tess-q9c5fg?file=/src/App.tsx
2. Notice the point at YUL that has a connection to YOW. This should only happen if the fit is set to something other than none.

Expected behaviour
The point is treated as an isolated point and not connected to an arbitrary point.

Screenshots

Version (please complete the following information):

• Elastic Charts: v61.0.0 prior versions are okay