[qt-iOS] QNetworkAccessManager doesn't recover after network is switched

Qt-5.7.0 iOS, request sent by QNetworkAccessManager will always return error after network is switched from WiFi to 4G. The sample program to reproduce this bug has been attached.
Before run the program, make sure you have a working WiFi network and 4G network enabled.
1) run the program, click 'Push Me' button, you will see the network
request's reply will be fetched and displayed in the window
2) Disable WiFi in your iPhone and the network will be switched to 4G,
click 'Push Me' button immediately, and you will see the network reply will
failed with UnknownNetworkError and will always fail in the rest of time.
Please note that you can't reproduce this bug 100%, please try several
times and I think you can reproduce it. Also sometimes when the network is
switched, the first network request's reply after the switch may never
finished which is also a bug.