[xcb] Multiple soundness issues

An issue was discovered in the xcb crate through 2021-02-04 for Rust. It has a soundness violation because bytes from an X server can be interpreted as any data type returned by xcb::xproto::GetPropertyReply::value.

References

• https://nvd.nist.gov/vuln/detail/CVE-2021-26956
• https://github.com/RustSec/advisory-db/issues/653
• https://rustsec.org/advisories/RUSTSEC-2021-0019.html
• https://github.com/advisories/GHSA-mp6r-fgw2-rxfx