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_6_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/9fab155c68a4e2164c39f61bc849ad669ad54f2c

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