pgsql: Clean up callers of JsonbIteratorNext().

Clean up callers of JsonbIteratorNext().

Coverity complained about the lack of a check on the return value in
parse_jsonb_index_flags' last call of JsonbIteratorNext.  Seems like
a reasonable gripe to me, especially since the code is depending on
that being WJB_DONE to not leak memory, so add a check.

In passing, improve a couple other places where the result was being
ignored, either by adding an assert or at least a cast to void.

Also, don't spell "WJB_DONE" as "0".  That's horrid coding style,
and it wasn't consistent either.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f8a187bdbae6e9d3b7407c0c37e3494518496200

Modified Files
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src/backend/utils/adt/jsonfuncs.c | 28 ++++++++++++++++------------
1 file changed, 16 insertions(+), 12 deletions(-)