[BUG] Potencial substraction overflow

[NEUZhangy]

Rust version: rustc 1.58.1 (db9d1b20b 2022-01-20)

Test case

add test for src/parser.rs::parse_number
#[test]
fn test_parse() {
let mut integer = vec![0u8];
let mut fraction = vec![0u8];
let data = 1;
let mut rdr = parse_number(integer.iter(), fraction.iter(), data);
}
error infor:
thread 'parse::test_parse' panicked at 'attempt to subtract with overflow', src/parse.rs:44:21
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace