users potential unaligned read

[dtolnay]

The users crate (in addition to being unmaintained for 3 years) contains this unsoundness: ogham/rust-users#55.

In some build modes, this is observable as a panic followed by abort:

thread 'main' panicked at 'misaligned pointer dereference: address must be a multiple of 0x8 but is 0x14480860b', /Users/dhruvkb/.cargo/registry/src/index.crates.io-6f17d22bba15001f/users-0.11.0/src/base.rs:297:34

thread 'main' panicked at 'panic in a function that cannot unwind', library/core/src/panicking.rs:126:5
thread caused non-unwinding panic. aborting.

In other build modes the UB may manifest in some other way, including the possibility of "working correctly" in some architectures. With RFC 3204 "Alignment niches for references types" and other compiler work, even the currently "working correctly" cases may deteriorate over time.

The affected code are the two *username here: https://github.com/ogham/rust-users/blob/d6883b4cc1bf00fdca920f5064ea551684fc0faf/src/base.rs#L297-L301.