pgsql: Fix pg_recvlogical for pre-10 versions

Fix pg_recvlogical for pre-10 versions

In e170b8c8, protection against modified search_path was added. However,
PostgreSQL versions prior to 10 does not accept SQL commands over a
replication connection, so the protection would generate a syntax error.

Since we cannot run SQL commands on it, we are also not vulnerable to
the issue that e170b8c8 fixes, so we can just skip this command for
older versions.

Author: Michael Paquier <michael@paquier.xyz>

Branch
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REL9_4_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/af5fbb1286cd4319db52835d4847175af9c2ed56

Modified Files
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src/bin/pg_basebackup/streamutil.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)