CVE-2019-16140: Use-after-free in chttp

The vulnerability stems from the From<Buffer> for Vec<u8> implementation where Vec::from_raw_parts was called on a temporary slice. The original code didn't account for slice ownership - when the slice went out of scope, it would deallocate the memory that the newly created Vec was referencing. The fix explicitly calls mem::forget(slice) to prevent this premature deallocation. The affected code is clearly shown in the pre-patch version of src/buffer.rs lines 192-195, making this the definitive vulnerable function.