Fix simple strict provenance cases in analysis/test

[kkysen]

Fixes #682.

More specifically, it fixes the low-hanging fruit of achieving strict provenance by replacing 0 as *{const,mut} _ with std::ptr::null{,_mut}(). The real int-to-ptr instances where std::ptr::from_exposed_addr and ptr::expose_addr() should be used I've left as is, though, as 1) strict provenance is still unstable and 2) that's what we currently emit. But removing the 0 as *{const,mut} _ makes the miri output much easier to deal with.