Application crash on start on iOS 7.1

Application sometimes crashes on start on iOS 7.1.

When QIOSScreen is created, [UIScreen screens] method is called to get screen objects. On iOS 7.1 this method sometimes returns empty array (Apple docs say that this method always returns at least one UIScreen object, the main screen, so this is bug in iOS 7.1).

It can be triggered by starting application via urlscheme, but reproduction rate isn't 100 %.

I wrote a patch that uses [UIScreen mainScreen] if [UIScreen screens] is empty and it works fine: http://pastebin.com/Mr6dYZUd

It's just a workaround, but there will be many iPad 4 devices with iOS 7.1, so Qt should use some workaround...