The problem was in calling GetLoadAddress on a value in the error state,
where `ValueObject::GetLoadAddress` could end up accessing the
uninitialized "address type" by-ref return value from `GetAddressOf`.
This probably happened because each function expected the other to
initialize it.
We can guarantee initialization by turning this into a proper return
value.
I've added a test, but it only (reliably) crashes if lldb is built with
ubsan.
e9fad0e91c