GHSA-f67m-9j94-qv9j Parser creates invalid uninitialized value

• crates.io hyper: < 0.14.12 → fixed in 0.14.12

Affected versions of this crate called `mem::uninitialized()` in the HTTP1 parser to create values of type `httparse::Header` (from the `httparse` crate). This is unsound, since `Header` contains references and thus must be non-null. The flaw was corrected by avoiding the use of `mem::uninitialized()`, using `MaybeUninit` instead.