Bar animation seems start from zero, ignoring actual axisMinimum

Bar animation seems start from zero, ignoring actual axisMinimum, so it took longer to finish
Found while reviewing #3650

## What did you expect to happen?
Bar animation should start from the actual minimum value

## What happened instead?

Seems always start from 0

## Charts Environment

**Charts version/Branch/Commit Number:**
**Xcode version:** 10
**Swift version:** 4.2

## Demo Project
data set:
```swift
func setDataCount(_ count: Int, range: Double) {
let yVals = [
BarChartDataEntry(x: 0, y: 10),
BarChartDataEntry(x: 1, y: 20),
BarChartDataEntry(x: 2, y: 30),
BarChartDataEntry(x: 3, y: 15)
]
```