Encoding error (code 5) - FileReader.readAsText on iOS 12.1.4

# Bug Report
Since iOS 12.1.4 we are having troubles to read files with FileReader.readAsText().

## Problem
readAsText returns null and an error with code 5 (encoding err?) will be thrown. No problems on android or former iOS version.

### What is expected to happen?
readAsText() normally ends with onloadend delivering the content of a file as a string.

### What does actually happen?
onloadend delivers null and onerror will be called aswell with the encoding err (code 5).

## Information
Same code - no problems at all

### Command or Code

### Environment, Platform, Device

### Version information

## Checklist

- [x] I searched for existing GitHub issues
- [x] I updated all Cordova tooling to most recent version
- [x] I included all the necessary information above

Start by reproducing FileReader.readAsText on iOS 12.1.4 and observe the onloadend and onerror callbacks. Compare the result with Android and earlier iOS versions; done means the file content is delivered as a string without the code 5 encoding error.

Written by the indexing model from the issue text.