InclusiveRange's size_hint can give 1 when empty, despite implementing TrustedLen

[scottmcm]

Repro:

#![feature(inclusive_range_syntax)]
#![feature(trusted_len)]

use std::iter::TrustedLen;

fn check_size_correctness<T:TrustedLen+ExactSizeIterator>(x: T) {
    let len = x.len();
    assert_eq!(x.count(), len);
}

fn main() {
    check_size_correctness(100...0u8);
}

#42134 will fix this, but I wanted to record it because I think TrustedLen being an unsafe trait means this could be leading to unsoundness.

[alexcrichton]

cc #42134, a fix