pgsql: Improve comment for att_isnull.

Improve comment for att_isnull.

The comment implies that a 1 in the null bitmap indicates a null value,
but actually a 0 in the null bitmap indicates a null value. Try to
be more clear.

Patch by me; proposed wording reviewed by Alvaro Herrera and Tom Lane.

Discussion: http://postgr.es/m/CA+TgmobHOP8r6cG+UnsDFMrS30-m=jRrCBhgw-nFkn0k9QnFsg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/221b377f09a30dd7c74c26c8c1db439afcc59141

Modified Files
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src/include/access/tupmacs.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)