pgsql: Allow width_bucket()'s "operand" input to be NaN.

Allow width_bucket()'s "operand" input to be NaN.

The array-based variant of width_bucket() has always accepted NaN
inputs, treating them as equal but larger than any non-NaN,
as we do in ordinary comparisons. But up to now, the four-argument
variants threw errors for a NaN operand. This is inconsistent
and unnecessary, since we can perfectly well regard NaN as falling
after the last bucket.

We do still throw error for NaN or infinity histogram-bound inputs,
since there's no way to compute sensible bucket boundaries.

Arguably this is a bug fix, but given the lack of field complaints
I'm content to fix it in master.

Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Reviewed-by: Dean Rasheed <dean(dot)a(dot)rasheed(at)gmail(dot)com>
Discussion: https://postgr.es/m/2822872.1750540911@sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/7374b3a53635cb031b4d1bedfd80531409f54693

Modified Files
--------------
src/backend/utils/adt/float.c | 18 +++++++++---------
src/backend/utils/adt/numeric.c | 17 +++++++----------
src/test/regress/expected/numeric.out | 16 ++++++++++++++--
src/test/regress/sql/numeric.sql | 2 ++
4 files changed, 32 insertions(+), 21 deletions(-)