Re: BUG #19603: Vuln47: distance_taxicab and distance_chebyshev silently return 0 instead of NaN when a cube coordin

Hi Ayush,

> Thanks for the report and repro.
>
> It looks to me like the root is distance_1D(): with a NaN coordinate none of
> its comparisons can be true, so it seems to fall through to the overlapping
> case and return 0. My first thought was to fix it there and return NaN when
> any endpoint is NaN, which seems enough for taxicab and Euclidean (<->), which
> accumulate with +=. Chebyshev needs a bit more, since its running max uses
> "d > distance" and NaN > x is false, so I added an explicit NaN check there too.

I noticed the patch on the commitfest and decided to take a look.

All in all it's good but there are several similar bugs that it
doesn't address (and which were not reported above):

```
=# CREATE EXTENSION cube;

=# SELECT '(1,1)'::cube = '(nan,nan)'::cube;
?column?
----------
t

=# SELECT '(nan)'::cube > '(1)'::cube; -- wrong because 'NaN' :: real
> 1.0 :: real
?column?
----------
f
```

I think it should.

--
Best regards,
Aleksander Alekseev