Before this change, `lhs == rhs` missed the check for
`lhs.size() == rhs.size()`, and then did a `memcmp` on the buffers up to
`lhs.size()`. This means that, if `lhs.size() < rhs.size()`, it would
allow two unequal strings to compare equal if, up to `lhs.size()` they
are the same; and if `lhs.size() > rhs.size()`, then it would read out
of bounds.