FV-ANC-3-CL10 Using ctx.remaining_accounts without non-zero data check

Bad

let extra_account = &ctx.remaining_accounts[0];
// No check for account liveness.

Good

let extra_account = &ctx.remaining_accounts[0];
let data = extra_account.try_borrow_data()?;
if data.iter().all(|&byte| byte == 0) {
    return Err(ProgramError::UninitializedAccount);
}