pgsql: Fix incorrect strictness test for ArrayCoerceExpr expressions.

Fix incorrect strictness test for ArrayCoerceExpr expressions.

The recursion in contain_nonstrict_functions_walker() was done wrong,
causing the strictness check to be bypassed for a parse node that
is the immediate input of an ArrayCoerceExpr node. This could allow,
for example, incorrect decisions about whether a strict SQL function
can be inlined.

I didn't add a regression test, because (a) the bug is so narrow
and (b) I couldn't think of a test case that wasn't dependent on a
large number of other behaviors, to the point where it would likely
soon rot to the point of not testing what it was intended to.

I broke this in commit c12d570fa, so back-patch to v11.

Discussion: https://postgr.es/m/27571.1550617881@sss.pgh.pa.us

Branch
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REL_11_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/93ec0c90cde7e0188c96bca9a8ba815b58c00d24

Modified Files
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src/backend/optimizer/util/clauses.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)