pgsql: Consistently truncate non-key suffix columns.

Consistently truncate non-key suffix columns.

INCLUDE indexes failed to have their non-key attributes physically
truncated away in certain rare cases. This led to physically larger
pivot tuples that contained useless non-key attribute values. The
impact on users should be negligible, but this is still clearly a
regression (Postgres 11 supports INCLUDE indexes, and yet was not
affected).

The bug appeared in commit dd299df8, which introduced "true" suffix
truncation of key attributes.

Discussion: https://postgr.es/m/CAH2-Wz=E8pkV9ivRSFHtv812H5ckf8s1-yhx61_WrJbKccGcrQ@mail.gmail.com
Backpatch: 12-, where "true" suffix truncation was introduced.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4b42a89938ac9d2ec06e9d831356407040e9094c

Modified Files
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src/backend/access/nbtree/nbtutils.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)