Potential underflow on userAmountStaked[token][msg.sender] in _withdraw

Handle 0xImpostor Vulnerability details Impact Underflowing userAmountStakedtokenmsg.sender once will let me exploit the entire token balance in the Staker contract. This can only be exploited if marketUnstakeFeee18 is ≥ 50%. Proof of Concept 1. Admin sets marketUnstakeFeee18 for this marketIndex...