Do not set ampm when the column doesn't exist

Editor assessment

The subject states both the condition and the avoided action, so a reader understands the fix without opening the diff. The fix(datetime) header matches a scoped bug fix in the datetime component. The body is absent, but the change is small and the 'fixes #22149' footer is well-formed and links the tracked issue, which is meaningful rather than noise. Style is clean: imperative phrasing, no trailing period, reasonable length. What is missing is any note on why the column can be absent, which would have lifted the teaching value, but nothing here misleads.