Sharia law: If a women can't prove rape will she get punished for that?

I was reading this post . I have a few question about it's contents, >A woman can imprisoned for admitting to pre-marital sex, because proving that a rape happened is next to impossible in Dubai, where four male Muslim witnesses are required. If a woman admits to being raped, and the rape cannot be proven by the legal system, the man or men walks free. If a woman tells she was raped and is not able to prove it, does it mean she engaged in pre-martial sex and will be punished for it? The answer says this, >If you're looking for the reason why this is the case even when they've been raped, it's because Islamic law, specifically, Sharia law, states that this is the punishment for engaging in pre-marital sex. As far as I know, this is definitely not the Islamic law. Islam would never punish an innocent. Can someone comment on this please.