[TIMOB-18163] iOS7: Alert with persistent: true locks up app when returning from multi-tasking

Issue Description

In iOS7 only (tested with iOS 8 without seeing this) when a user initiates multi-tasking (double tap home button to see all running apps) with an alert showing, if the user returns to the app, the alert disappears but the app is unusable, due to the semi-transparent "shield" remaining from the alert.

Steps to reproduce

1. Launch the application 2. Tap on the button (an alert should be displayed) 3. Background the application by doing double-tap on the Home button.

Expected behavior:

When selecting the app again on the recently used apps screen, the alert will be shown again.

Current behavior:

The app shows the alert for a second before it disappears, making it impossible to use the app unless the user sends the app to the background and then to the foreground again.

Tested on

Tested on iPad Air and iPhone Simulators with Ti SDK 3.4.1.GA

Sample Code

Titanium.UI.setBackgroundColor('#000');
var win1 = Titanium.UI.createWindow({
	title : 'Window',
	backgroundColor : '#fff'
});

var button = Titanium.UI.createButton({
	title : 'Click Me!!!',
	width : 200,
	height : 100
});

var alert = Titanium.UI.createAlertDialog({
	persistent : true,
	message : "Should be persistent always but I'm not working properly when double-clicking the home button on iPad!!!",
	ok : 'Okay',
	title : 'Am I persistent?'
});

button.addEventListener('click', function() {
	alert.show();
});

win1.add(button);
win1.open();