[iOS] WKWebview - Back button in location bar is always enabled

### Issue Type

- [x] Bug Report

## Description
Click on back button of location bar or `history.back()` or `history.go(-1)`, the back button of location bar is always enabled. User can click on back button or call `history.back()` or `history.go(-1)`, with no endpoint.

It looks like the back action always pushes new URL to history stack instead going back

## Information
I'm using `usewkwebview=yes`. When open inappbrowser in the first time, back button is disabled. But when click on some URL, the back button is always enabled.

I checked this function in CDVWKInAppBrowser.m
```
- (void)webView:(WKWebView *)theWebView didFinishNavigation:(WKNavigation *)navigation
```

`theWebView.canGoBack;` is always returns true after the first redirect

### Command or Code
```
const target = '_blank';
const options = [
'location=yes',
'hidden=no',
'hideurlbar=no',
'toolbar=yes',
'hidenavigationbuttons=no',
'zoom=no',
'transitionstyle=crossdissolve',
'enableViewportScale=yes',
'usewkwebview=yes',
'beforeload=get'
];
inAppBrowserRef = window.cordova.InAppBrowser.open(url, target, options.join());
```

### Environment, Platform, Device
Cordova ver 9

Platform: iOS 13,
Device: iPhone 7

package.json
cordova-plugin-inappbrowser: "3.1.0"
cordova-plugin-wkwebview-engine: "1.2.1"

## Checklist

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

Start in CDVWKInAppBrowser.m at webView:didFinishNavigation: and reproduce with usewkwebview=yes using the provided in-app browser options. Check how theWebView.canGoBack is evaluated after the first redirect and compare it with history.back() and history.go(-1). Done means the location-bar back button and history actions are disabled at the navigation endpoint and enabled only when a prior page exists.

Written by the indexing model from the issue text.