Fixed an issue that cause crash when a user taps on front facing camera to focus.
Fixed an issue that cause crash when a user taps on front facing camera to focus.

jpipard/DKImagePickerController,zhangao0086/DKImagePickerController,zhangao0086/DKImagePickerController,North-American-Signs/DKImagePickerController,metasmile/DKImagePickerController,gorjuspixels/DKImagePickerController,jpipard/DKImagePickerController,gorjuspixels/DKImagePickerController,North-American-Signs/DKImagePickerController,metasmile/DKImagePickerController