Function itertools::size_hint::mul

pub fn mul(
    a: (usize, Option<usize>),
    b: (usize, Option<usize>)
) -> (usize, Option<usize>)

Multiply SizeHint correctly

use std::usize;
use itertools::size_hint;

assert_eq!(size_hint::mul((3, Some(4)), (3, Some(4))),
           (9, Some(16)));

assert_eq!(size_hint::mul((3, Some(4)), (usize::MAX, None)),
           (usize::MAX, None));

assert_eq!(size_hint::mul((3, None), (0, Some(0))),
           (0, Some(0)));