[#5286] Skip orphaned blog posts in nbhd blog posts macro

- If a blog posts app has been deleted, but the post still
  exists in mongo, technically it's deleted anyway, and
  shouldn't be included in the macro output.

- This is a side-effect of old code that didn't clean up artifacts
  properly on tool deletion. The code as it is today *does*
  delete artifacts when the tool is deleted.