pgpool: Fix buffer overflow error in show pool_status.

Fix buffer overflow error in show pool_status.

"show pool_status", "pgpool show" and pcp_pool_status could cause a
buffer overflow error. If backend_flag is set to "ALWAYS_PRIMARY",
pool_flag_to_str(), which is responsible to produce printable format
of backend_flag, wrote data past to the end of static buffer.

Author: Tatsuo Ishii <ishii(at)postgresql(dot)org>
Reported-by: zam bak <zam6ak(at)gmail(dot)com>
Reviewed-by: Bo Peng <pengbo(at)sraoss(dot)co(dot)jp>
Discussion: https://www.postgresql.org/message-id/20251202.140205.427777414210613577.ishii%40postgresql.org
Backpatch-through: v4.3

Branch
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V4_4_STABLE

Details
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https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=8337221c31e6342cde67bb9caffc72522a07a65b

Modified Files
--------------
src/config/pool_config.l | 4 ++--
src/config/pool_config_variables.c | 4 ++--
2 files changed, 4 insertions(+), 4 deletions(-)