Re: casting operand to proper type in BlockIdGetBlockNumber

I wrote:
> Andres Freund <andres(at)anarazel(dot)de> writes:
>> We should fix these passing-null-pointer cases...

> Yeah, working on that now.

The attached is enough to get through check-world with
"-fsanitize=undefined" using RHEL8's clang 12.0.1.
Most of it is the same old null-pointer-with-zero-count
business, but the change in numeric.c is a different
issue: "ln(-1.0)" ends up computing log10(0), which
produces -Inf, and then tries to assign that to an integer.
We don't actually care about the garbage result in that case,
so it's only a sanitizer complaint not a live bug.

I'm not sure whether to back-patch --- looking through the
git logs, it seems we've back-patched some fixes like these
and not others. Thoughts?

In any case, if we're going to take this seriously it seems
like we need a buildfarm machine or two testing this option.

regards, tom lane