subtract overflow on fmt::Display on BigDecimal

[austinabell]

when trying to print a decimal with a very large negative scale and abs value of the integer length overflow usize::MAX, the print will panic.

Repro:

    let a = BigDecimal::new(bigdecimal::num_bigint::BigInt::from(1), i64::MIN);
    println!("{:?}", a);

The line I'm inferring is the issue here is

bigdecimal-rs/src/lib.rs

Line 1566 in 272123e

let location = abs_int.len() as i64 - self.scale;

(could be wrong, didn't verify)