ComparePerformance: fix crash in RTJO mode

[d10c]

With --dynamic-join-order-mode=all, both first and second are
undefined, leading to a crash. Until RTJO mode gets proper tuple
counting, this change prevents a crash when unfurling the steps of a
predicate.

[Copilot]

PR Overview

This PR addresses a crash in RTJO mode by ensuring that when both "first" and "second" are undefined, the code safely defaults to an empty array instead of attempting to access a property on an undefined object. Key changes include updating the default for steps in the predicate row component to prevent a crash.

• Replace non-null assertion on "second" with safe optional chaining.
• Provide an empty array as fallback to ensure safe iteration with map.

Changes

File	Description
extensions/ql-vscode/src/view/compare-performance/ComparePerformance.tsx	Updated the steps extraction to safely handle undefined values and prevent a crash in RTJO mode

Copilot reviewed 1 out of 1 changed files in this pull request and generated no comments.

Comments suppressed due to low confidence (1)

extensions/ql-vscode/src/view/compare-performance/ComparePerformance.tsx:801

• Ensure that using an empty array as the default value for steps covers all expected cases, and consider adding an inline comment to explain why the empty array fallback is necessary to prevent crashes when both 'first' and 'second' are undefined.

{abbreviateRASteps(first?.steps ?? second?.steps ?? []).map(

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[asgerf]

LGTM and I wrote the affected code; though someone with merge rights will need to approve