Quick fix to prevent panic on nil collector result

[nvanthao]

Description, Motivation and Context

Fixes: https://github.com/replicatedhq/troubleshoot/issues/1442

Quick fix before we can refractor the collector, I think we should not mutate the result in defer block.

Checklist

• [x] New and existing tests pass locally with introduced changes.
• [ ] Tests for the changes have been added (for bug fixes / features)
• [ ] The commit message(s) are informative and highlight any breaking changes
• [ ] Any documentation required has been added/updated. For changes to https://troubleshoot.sh/ create a PR here

Does this PR introduce a breaking change?

• [ ] Yes
• [x] No