Fix --xl -r extracting code from oldest response instead of most recent

[ikatyal2110]

When a conversation has multiple responses and you run llm logs --xl -r, the extracted code block comes from the oldest response in the conversation rather than the most recent one. This happens because the extract loop iterates rows from the start (oldest after the DESC-then-reverse ordering), while -r correctly reads from rows[-1] (newest). The fix restricts the search to rows[-1] when -r is active, so both flags operate on the same response. Fixes #821.