iOS: Crash when opening menus in QtQuickControls

Found crash when testing package Qt-5.7.0-334 (and also when testing Qt-5.7 branch from repo).

If running e.g texteditor example in qtquickcontrols, you will get a crash when trying to open e.g the file menu or a combobox, and then close it.
The offending patch that introduced it: e78ca787a (qtbase). https://code.qt.io/cgit/qt/qtbase.git/commit/?id=e78ca787a

The reason for the crash is that QIOSTextResponder will (after the patch) clear the focus object immediately after opening a menu. This is wrong, since the menu would normally close again when changing focus object, except since this happens while the menu is about to open, it is unexpected and leaves QIOSMenu in a wrong state.