Fix to check-in [b9190d3da70c4171] - the agg-with-indexed-expr optimization

Fix to check-in [b9190d3da70c4171] - the agg-with-indexed-expr optimization
requested by ticket [99378177930f87bd] - that can cause an incorrect answer
if an aggregate subquery has a GROUP BY clause, and that GROUP BY contains a
term that is not in the result set, and the outer query makes use of expression
indexes.  Problem reported by
[forum:/forumpost/a68313d054|forum post a68313d054].

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