When a gambler tells you he's borrowing money to gamble, he's implicitly warning you that if he loses, repaying the loan might be difficult, and you could end up sharing the loss. As someone with my mindset, I should be cautious and well-informed in such situations.
As long as you don't lend money to someone to gamble, you don't have to be afraid when someone else invites you to gamble with that kind of money. Because the person who has to return the money is the borrower, not you unless you have made a promise to return the money together when you lose at gambling. But if you are only invited and are not told about it by the person who invited you, I think you are free from anything so you don't have to bear paying the money.