inclusion: RoundUpByMultipleOf and all other modulo denominator must be checked for zero before usage

[odeke-em]

If we examine

go-square/inclusion/blob_share_commitment_rules.go

Lines 44 to 47 in 4e84d80

	func RoundUpByMultipleOf(cursor, v int) int {
	if cursor%v == 0 {
	return cursor
	}

we see that an outside modulus is being used. Let's bullet proof by firstly checking if the denominator is zero and about a runtime panic of divide by zero

[rootulp]

Agreed. I think you're proposing something like:

// RoundUpByMultipleOf rounds cursor up to the next multiple of v. If cursor is divisible
// by v, then it returns cursor.
func RoundUpByMultipleOf(cursor, v int) (int, error) {
	if v == 0 {
		return 0, fmt.Errorf("v cannot be 0")
	}
	if cursor%v == 0 {
		return cursor, nil
	}
	return ((cursor / v) + 1) * v, nil
}

which is API breaking but IMO seems reasonable.