Fixed issue with TouchId and hasValueForKey:

## TouchID issue: 
There is a problem when updating an item that was stored with touchId. SecItemUpdate() is not 
allowed on such items. See Known Issues in https://developer.apple.com/library/ios/releasenotes/General/RN-iOSSDK-8.0/

## hasValueForKey: 
Always returned NO, when the key was != null.