pgsql: Repair bug #2694 concerning an ARRAY[] construct whose inputs are

Log Message:
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Repair bug #2694 concerning an ARRAY[] construct whose inputs are empty
sub-arrays.  Per discussion, if all inputs are empty arrays then result
must be an empty array too, whereas a mix of empty and nonempty arrays
should (and already did) draw an error.  In the back branches, the
construct was strict: any NULL input immediately yielded a NULL output;
so I left that behavior alone.  HEAD was simply ignoring NULL sub-arrays,
which doesn't seem very sensible.  For lack of a better idea it now
treats NULL sub-arrays the same as empty ones.

Tags:
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REL8_0_STABLE

Modified Files:
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    pgsql/src/backend/executor:
        execQual.c (r1.171.4.1 -> r1.171.4.2)

(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/executor/execQual.c.diff?r1=1.171.4.1&r2=1.171.4.2)