[TIMOB-27481] Android: Navigating back from camera overlay can wrongly close the app

When a Camera activity with an overlay is opened from the first window in an application and the system's back button is pressed the application gets closed. *Test code:* _app.js_

var win = Ti.UI.createWindow(),
	button = Ti.UI.createButton({ title: 'Camera' });
button.addEventListener('click', function () {
	Ti.Media.showCamera({
		overlay: getOverlay()
	});
});
win.add(button);
win.open();

function getOverlay() {
	var view = Ti.UI.createView({
		backgroundColor: '#55990000',
	});
	return view;
}

Opening a camera activity from another window and clicking back works as expected - only the camera activity is closed. One reason this may happen is that the camera activity with an overlay does not have a WindowProxy child and this raises the exitOnClose flag when we go back from it with only one window in the stack.