Performance hit between V3.2.1 and V3.0.2

## What did you do?

I compare V3.0.2 and 3.2.1

## What did you expect to happen?

the same performance

## What happened instead?

Not the same performance

## Charts Environment

**Charts version/Branch/Commit Number:**
**Xcode version:Version 10.1 beta 3 (10O45e)
**Swift version:3 and 4.2
**Platform(s) running Charts:OSX
**macOS version running Xcode:10.14

## Demo Project

the file source for the graph Line is the same for the 2 versions
with V3.2.1 that's not really good

[charts mov 302 and 321.zip](https://github.com/danielgindi/Charts/files/2491269/charts.mov.302.and.321.zip)

ℹ Please link to or upload a project we can download that reproduces the issue.

Start with the uploaded charts.mov.302.and.321.zip demo project and reproduce the comparison between Charts V3.0.2 and V3.2.1 on the stated macOS/Xcode environment. Profile the same Line graph workload in both versions to identify the regression; done means the cause is isolated and performance is restored or the difference is explained.

Written by the indexing model from the issue text.