pgsql: Further tweaking of width_bucket() edge cases.

Further tweaking of width_bucket() edge cases.

I realized that the third overflow case I posited in commit b0e9e4d76
actually should be handled in a different way: rather than tolerating
the idea that the quotient could round to 1, we should clamp so that
the output cannot be more than "count" when we know that the operand is
less than bound2.  That being the case, we don't need an overflow-aware
increment in that code path, which leads me to revert the movement of
the pg_add_s32_overflow() call.  (The diff in width_bucket_float8
might be easier to read by comparing against b0e9e4d76^.)

What's more, width_bucket_numeric also has this problem of the quotient
potentially rounding to 1, so add a clamp there too.

As before, I'm not quite convinced that a back-patch is warranted.

Discussion: https://postgr.es/m/391415.1680268470@sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/a2a0c7c29e47f39da905577659e66b0086b769cc

Modified Files
--------------
src/backend/utils/adt/float.c         | 69 ++++++++++++++++++++++-------------
src/backend/utils/adt/numeric.c       | 17 +++++++--
src/test/regress/expected/numeric.out | 25 +++++++++++++
src/test/regress/sql/numeric.sql      |  5 +++
4 files changed, 88 insertions(+), 28 deletions(-)