ChartData::getDataSetByLabel always return the first IChartDataSet when ignorecase = true

[PeterKaminski09]

• I've read, understood, and done my best to follow the *CONTRIBUTING guidelines.

Issue

It appears that this commit (https://github.com/danielgindi/Charts/pull/3892/files) added the comparison label.caseInsensitiveCompare(label) to ChartData::getDataSetByLabel.

This will always be true, so statements like chartData.getDataSetByLabel("myLabel", ignorecase: true) will return whatever IChartDataSet is at index 0.

Effected code

 internal func getDataSetIndexByLabel(_ label: String, ignorecase: Bool) -> Int
    {
        // TODO: Return nil instead of -1
        if ignorecase
        {
            return dataSets.firstIndex {
                guard let label = $0.label else { return false }
                return label.caseInsensitiveCompare(label) == .orderedSame
            } ?? -1
        }
        ...
    }

Follow-up

I'm happy to submit a pull-request to fix this issue 😺

Charts Environment

Charts version/Branch/Commit Number: 3.4.0
Xcode version: 11.3.1
Swift version: 5.0
Platform(s) running Charts: iOS
macOS version running Xcode: 10.15.2