pgsql: Make walsender always initialize the buffers.

Make walsender always initialize the buffers.

Walsender uses the local buffers for each outgoing and incoming message.
Previously when creating replication slot, walsender forgot to initialize
one of them and which can cause the segmentation fault error. To fix this
issue, this commit changes walsender so that it always initialize them
before it executes the requested replication command.

Back-patch to 9.4 where replication slot was introduced.

Problem report and initial patch by Stas Kelvich, modified by me.
Report: https://www.postgresql.org/message-id/A1E9CB90-1FAC-4CAD-8DBA-9AA62A6E97C5@postgrespro.ru

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/feb659cced9755966190bbabfcead54fcfcddf0e

Modified Files
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src/backend/replication/walsender.c | 18 ++++++++----------
1 file changed, 8 insertions(+), 10 deletions(-)