BeamMusicPlayerExample crashes on launch on iPad running iOS 5.1.1 (9B206)

[ruohoruotsi]

The issue is that in Source/BeamMusicPlayerViewController.m : viewDidLoad, the calls to setVolumeThumbImage:forState:, setMinimumVolumeSliderImage:forState:, setMaximumVolumeSliderImage:forState: are only NS_AVAILABLE_IOS(6_0).

Because the iOS deployment target is 5.0, there should be a runtime check that MPVolumeView instancesRespondToSelector:, to avoid crashes on and to properly support an iOS 5.0.