Replace NULL with nullptr

[wdoekes]

I don't c++ on a regular basis. This new(std::nothrow) business is new (haha) to me.

If all new's are supposed to throw bad_alloc then most of the c++ style code allocation is broken.

I don't see any -fno-exceptions anywhere, and I don't see any explicit operator new override using malloc() either. So I assume normal new failures will return in an unhandled exception and an abort().

[orgads]

@wdoekes I marked them as won't fix to silence the checker, and pushed a fixing follow-up commit to https://github.com/orgads/sipp/tree/less-null-validations.

I'll open a PR after this one is merged, since it is a dependency.