FIX CroppedFocusedImage failure case
FIX CroppedFocusedImage failure case

Stop issue where CroppedFocusedImage() doesn't handle the failure case like 'Image::getFormattedImage', as that function implicitly returns null if it cannot find the asset. (#35)
jonom/silverstripe-focuspoint,jonom/silverstripe-focuspoint