[Audit] RejectionSample superfluous loop condition

[AnomalRoil]

Here the for loop depends on the condition zero.Cmp(q) == -1, however neither q nor zero are modified inside the loop, so this check can be moved out of the loop:

func RejectionSample(q *big.Int, eHash *big.Int) *big.Int { // e' = eHash
    qBits := q.BitLen()
    // e = the first |q| bits of e'
    e := firstBitsOf(qBits, eHash)
    // while e is not between 0-q
    for !(e.Cmp(q) == -1 && zero.Cmp(q) == -1) {
        eHash := SHA512_256i(eHash)
        e = firstBitsOf(qBits, eHash)
    }
    return e
}