pgsql: Plug memory leak in index_get_partition

Plug memory leak in index_get_partition

The list of indexes was being leaked when asked for an index that
doesn't have an index partition in the table partition. Not a common
case admittedly --and in most cases where it occurs, caller throws an
error anyway-- but worth fixing for cleanliness and in case any
third-party code is calling this function.

While at it, remove use of lfirst_oid() to obtain a value we already
have.

Author: Justin Pryzby <pryzby(at)telsasoft(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/20201105203606.GF22691@telsasoft.com

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/d94d37f8c0c77cf1b9c5ae924bb6cfc12f4bc692

Modified Files
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src/backend/catalog/partition.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)