Flutter返回IOS，onPageFinished没有回调

## Steps to Reproduce
我使用的是官方提供的example_swift，进行原生跳转flutter的试验，从Flutter跳转回来后，并未回调onPageFinished

class ViewController: UIViewController {

override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view.
}

@IBAction func onClickPushFlutterPage(_ sender: UIButton, forEvent event: UIEvent){
FlutterBoostPlugin.open("first", urlParams:[kPageCallBackId:"MycallbackId#1"], exts: ["animated":true], onPageFinished: { (_ result:Any?) in
print(String(format:"call me when page finished, and your result is:%@", result as! CVarArg));
}) { (f:Bool) in
print(String(format:"page is opened"));
}
}
@IBAction func onClickPresentFlutterPage(_ sender: UIButton, forEvent event: UIEvent){
FlutterBoostPlugin.present("second", urlParams:[kPageCallBackId:"MycallbackId#2"], exts: ["animated":true], onPageFinished: { (_ result:Any?) in
print(String(format:"call me when page finished, and your result is:%@", result as! CVarArg));
}) { (f:Bool) in
print(String(format:"page is presented"));
}
}
}

**Flutter Boost Version**
1.17.1，Flutter VERSION: 1.22.1
Flutter
**Target Platform:**
iOS 10
**Target OS version/browser:**
IOS 13.6
**Devices:**
IPHONE 7

## Logs
**Flutter Boost Version**
1.17.1，Flutter VERSION: 1.22.1
Flutter
**Target Platform:**
iOS 10
**Target OS version/browser:**
IOS 13.6
**Devices:**
IPHONE 17

Start by reproducing the issue in the repository's example_swift app with FlutterBoostPlugin.open and present, then trace the iOS callback path for onPageFinished when returning from Flutter. Compare the behavior on Flutter Boost 1.17.1 and Flutter 1.22.1; done means the callback fires with the page result after returning for both navigation methods.

Written by the indexing model from the issue text.