[16.0] evalengine: TypeOf for Columns should only use value type when we have a value

[systay]

Description

While working on other parts of Vitess, we noticed this issue. Difficult to show the bug using end to end tests, but the unit test should show the behaviour we want.

Related Issue(s)

Issue: #13149
Backport of: #13148

Checklist

• "Backport to:" labels have been added if this change should be back-ported
• Tests were added or are not required
• Did the new or modified tests pass consistently locally and on the CI
• Documentation was added or is not required

[vitess-bot]

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