Fix KeepAlive null error

[mustafayildiz12]

Versions:
flutter: 3.32.0
flutter_inappwebview: ^6.1.5

Error:

Fatal Exception: java.lang.RuntimeException
Unable to destroy activity {com.limakteknoloji.limakmobile/com.limakteknoloji.limakmobile.MainActivity}: java.lang.NullPointerException: Attempt to read from field 'java.lang.String com.pichillilorenzo.flutter_inappwebview_android.webview.in_app_webview.FlutterWebView.keepAliveId' on a null object reference in method 'void com.pichillilorenzo.flutter_inappwebview_android.webview.InAppWebViewManager.dispose()'

Issue Scenario:

1. This error happens ın android devices only.
2. If you use keepAlive and try to dispose it, you will get this error when app is terminated.

After getting this NullPointerException I checked the current code and saw this issue in InAppWebViewManager.java

Just use ;

keepAliveWebViews.remove(keepAliveId);

instead of;

if (keepAliveWebViews.containsKey(keepAliveId)) {
keepAliveWebViews.put(keepAliveId, null);
}

Tested on android 12, 13, 14.