pgsql: Fix optimization for skipping searches for parallel-query hazard

Fix optimization for skipping searches for parallel-query hazards.

Fix thinko in commit da1c91631: even if the original query was free of
parallel hazards, we might introduce such a hazard by adding PARAM_EXEC
Param nodes.  Adjust is_parallel_safe() so that it will scan the given
expression whenever any such nodes have been created.  Per report from
Andreas Seltenreich.

Discussion: <878tse6yvf.fsf@credativ.de>

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/4324ade9a6880113b08070305482ace2e8a2617c

Modified Files
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src/backend/optimizer/util/clauses.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)