FIX: ensures successive topic hydrates doesn't override category (PR #12865)

This bug has first been seen when loading similar topics, minimum repro:

  • Have a topic named “Something Foo Bar” with a category.

  • Call this in console:"similar-topic", { title: "Something foo bar", raw: "" })
  • Navigate to latest (no full refresh)

  • The category from the topic should have disappeared


Very nice find.