message: fix: Superset logo link when logged out
  Closes
diff: <span class="icon-bar"></span>
  <span class="icon-bar"></span>
  </button>
  - <a class="navbar-brand" href="/superset{{ logo_target_path }}">
  + <a class="navbar-brand" href="{{ '/superset' + logo_target_path if current_user.username is defined else '#' }}">
  <img
  width="{{ app_icon_width }}"
  src="{{ appbuilder.app_icon }}"
  