Fix infinite while loop when buf size is less than 3

[kailes]

No description provided.

[6xzo]

If you add these additional cases to the tests, they hang without this fix.

    #[test]
    fn test_get_unknown() {
        let buf = [];
        assert!(crate::get(&buf).is_none());
// new cases:
        let buf = [0x31];
        assert!(crate::get(&buf).is_none());
        let buf = [0x31, 0x32];
        assert!(crate::get(&buf).is_none());
    }

[kailes]

@bojand Hi, have some time to review this?

[bojand]

Hello, thanks for the PR. This should be available in v0.12.0.