No translation that I've ever seen translates it that way. Qur'an corpus online (the best source for comparative English translations) shows every translation the same, with no (if not) parenthetical.
http://corpus.quran.com/translation.jsp?chapter=24&verse=33In other words, the (if not) looks completely (made up) and (isn't in the actual text).
You can have fun with such parentheticals, which are common in the (often incomprehensible) Qur'an while relatively rarely being used for translating other religious texts.
For example, "Muhammad is not the father of any of your men, but (is not) the messenger of Allah, and (is not) the seal of the prophets: and Allah (does not) have full knowledge of all things."