number_to_human_size broken if current locale doesn't define number.format.separator or number.human.format.separator

number_to_human_size kinda breaks, if neither precision/separator/delimiter are passed in options[] nor is there a corresponding translation for number.format.separator or number.human.format.separator in the current translation.

Example:

I18n.locale = 'en-US'
helper.number_to_human_size(1024**3) #=> "1 GB"
I18n.locale = 'KLINGON'
helper.number_to_human_size(1024**3) #=> 1.0

For the sake of backward compatibility with code that calls number_to_human_size with a single numeric argument when no translations for the aforementioned are available in the current locale, I think providing hardcoded fallback default for precision/separator/delimiter is reasonable.