Resolves#7878
An empty repository topic was not stored consistently across databases, this caused the `ONLY_SHOW_RELEVANT_REPOS` feature to not work correctly. Always store empty repository topics as an empty array to fix this.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7920
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: Maks1mS <maks1ms@noreply.codeberg.org>
Co-committed-by: Maks1mS <maks1ms@noreply.codeberg.org>
