Bar chart crashes when two data sets have different numbers of entries

* [✅ ] 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?

1. Create a `BarChart`
2. Create two data sets, each with a different number of entries.
3. Put the two data sets into a `BarChartData` class.
4. Load the `BarChartData` into the `BarChart`
5. Display the `BarChart` on the screen.

## What did you expect to happen?

I expect the bar chart to display correctly on the screen.

## What happened instead?

The Charts library crashed my application.

## Charts Environment

**Charts version/Branch/Commit Number:** 4.0.1 release
**Xcode version:** 12.4 12D4e
**Swift version:** 5.1
**Platform(s) running Charts:** iOS
**macOS version running Xcode:**

## Demo Project
https://github.com/fire-at-will/charts-bug

## Screenshot

https://imgur.com/a/8VQl6PA

## Fix

A PR fixing this issue has been submitted: https://github.com/danielgindi/Charts/pull/4634

Update April 25, 2021: Added PR fix link.