pgsql: Fix comment on when HOT update is possible.

Fix comment on when HOT update is possible.

The conditions listed in this comment have changed several times, and at
some point the thing that the "if so" referred to was negated.

The text was OK up to 9.6. It was differently wrong in v10, v11 and
master, so fix in all those versions.

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d7bf9ad8431700763a135710e2685317c67e25bc

Modified Files
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src/backend/access/heap/heapam.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)