pgsql: Fix incorrect error message in libpq_pipeline

Fix incorrect error message in libpq_pipeline

One of the tests for the pipeline mode with portal description expects a
non-NULL PQgetResult, but used an incorrect error message on failure,
telling that PQgetResult being NULL was the expected result.

Author: Jelte Fennema
Discussion: https://postgr.es/m/CAGECzQTkShHecFF+EZrm94Lbsu2ej569T=bz+PjMbw9Aiioxuw@mail.gmail.com
Backpatch-through: 14

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f69a7f08fd01aa7d6dcd2c34dbdc4eb154a5ec12

Modified Files
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src/test/modules/libpq_pipeline/libpq_pipeline.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)