PoC: possible repro for issue 69

[danburkert]

[oconnor663]

It looks like this would reproduce the scenario, yes, though I don't know if I'd actually expect it to crash. @Gankro (by the power of git blame I summon thee), do you know what actually happens if we violate the rules set out in ptr::add's docs, and add an offset larger than isize::MAX? All the context on why I'm asking this is in https://github.com/danburkert/memmap-rs/issues/69.

[Gankra]

It's Undefined Behaviour and llvm is permitted to do anything and everything to your code if you do it