pgsql: Add 'Portal Close' message to pipelined PQsendQuery()

Add 'Portal Close' message to pipelined PQsendQuery()

Commit acb7e4eb6b1c added a new implementation for PQsendQuery so that
it works in pipeline mode (by using extended query protocol), but it
behaves differently from the 'Q' message (in simple query protocol) used
by regular implementation: the new one doesn't close the unnamed portal.
Change the new code to have identical behavior to the old.

Reported-by: Yura Sokolov <y.sokolov@postgrespro.ru>
Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Discussion: https://postgr.es/m/202106072107.d4i55hdscxqj@alvherre.pgsql

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/4efcf47053eaf8dd88de2b1a89478df43d37d5c0

Modified Files
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src/interfaces/libpq/fe-exec.c                              | 8 +++++++-
src/test/modules/libpq_pipeline/traces/pipeline_abort.trace | 2 ++
2 files changed, 9 insertions(+), 1 deletion(-)