Fixes crash when user refuses camera access on iOS 8
Fixes crash when user refuses camera access on iOS 8

The first time AVCaptureDeviceInput creation will present a
dialog to the user requesting camera access. If the user refuses
the creation fails.

See WWDC 2013 session #610 for details, but note this behaviour
does not seem to be enforced on iOS 7 where as it is with iOS 8.

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