Unsplit an empty but with non-zero capacity BytesMut doesn't work

[songzhi]

let mut bytes = BytesMut::with_capacity(32);
unsafe {
    bytes.set_len(16);
}
let mut rest = bytes.split_off(16);
// unsafe {
//     rest.set_len(8);
// }
println!("{}", rest.capacity()); // 16
bytes.unsplit(rest);
println!("{}", bytes.capacity()); // 16, but it should be 32

if I uncomment rest.set_len(8), the result would be right. I think the following logic is wrong. It just check length, the capacity should be checked too.

bytes/src/bytes_mut.rs

Lines 821 to 824 in 6fdb739

	fn try_unsplit(&mut self, other: BytesMut) -> Result<(), BytesMut> {
	if other.is_empty() {
	return Ok(());
	}