pgsql: Small cleanups in SQL/JSON code

Small cleanups in SQL/JSON code

These are to keep Coverity happy. In one case remove a redundant NULL
check, and in another explicitly ignore a function result that is already
known.

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/f7a605f636d62935b80f9905575d40bc4eeca5ae

Modified Files
--------------
src/backend/parser/parse_expr.c | 2 +-
src/backend/utils/adt/jsonb.c   | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)