release-22.1: colbuilder: fix planning with no aggregate funcs in non-scalar context

[blathers-crl]

Backport 1/1 commits from #87451 on behalf of @yuzefovich.

/cc @cockroachdb/release

---

Previously, in a case when the aggregator doesn't have any aggregate functions to evaluate, we would replace it with a special "fixed num tuples" operator, with the number of tuples always set to 1. But that is only correct if the aggregator is in scalar context - in the non-scalar context we should return no tuples. The bug has been present since forever, and I couldn't come up with a repro without disabling some of the optimizer rules, so it seems unlikely to occur in production, thus, there is no release note.

Fixes: #87434.

Release justification: bug fix.

Release note: None

---

Release justification:

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[msirek]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @mgartner)