Crash at BarLineScatterCandleBubbleRenderer.swift

* [ X] I've read, understood, and done my best to follow the [*CONTRIBUTING guidelines](https://github.com/jjatie/Charts/blob/master/CONTRIBUTING.md).

## What did you do?

Implemented the SDK by SPM,
I'm using the LineChartView with two datasets that are updated by the view in real-time -
1. linear
2. stepped

## What did you expect to happen?

Two lines in the chart constantly updating, No crashes

## What happened instead?

Crashlytics reports 3% crashes in BarLineScatterCandleBubbleRenderer.swift -
Crashed: com.apple.main-thread
BarLineScatterCandleBubbleRenderer.swift - Line 4344645012
LineChartRenderer.drawCircles(context:) + 4344645012

## Charts Environment

**Charts version/Branch/Commit Number:*4.0.1*
**Xcode version:*12.5*
**Swift version:*5*
**Platform(s) running Charts:*iOS*
**macOS version running Xcode:*11.4*

## Demo Project

Unavailable

Start with BarLineScatterCandleBubbleRenderer.swift, especially drawCircles(context:), and review the reported Crashlytics stack location. Reproduce the issue with a LineChartView using linear and stepped datasets updated in real time on Charts 4.0.1. Done means the same workload no longer crashes; no demo project is available in the report.

Written by the indexing model from the issue text.