pgsql: Fix minor memory leak in pg_dump

Fix minor memory leak in pg_dump

A query used to read default ACL information from the catalogs did not
free a set of PQExpBuffer.

Oversight in commit e2090d9, so backpatch down to 9.6.

Author: Jie Zhang
Reviewed-by: Sawada Masahiko
Discussion: https://postgr.es/m/05bcbc5857f948efa0b451b85a48ae10@G08CNEXMBPEKD06.g08.fujitsu.local
Backpatch-through: 9.6

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d70c014624dda9cd78bd4664c291a6627efca23f

Modified Files
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src/bin/pg_dump/pg_dump.c | 5 +++++
1 file changed, 5 insertions(+)