message: trivial fix, don't unregister reader if detached
diff: @@ -202,6 +202,9 @@ void SlabAlloc::detach() noexcept
  // placed correctly (logically) after the end of the file.
  m_slabs.clear();
  clear_freelists();
  +#if REALM_ENABLE_ENCRYPTION
  + m_realm_file_info = nullptr;
  +#endif
  m_attach_mode = attach_None;
  }
  