fix(nbp): Add redirect to root when unauthorized on /users/nbp_wallet/*

Usually, when the current user is not logged in and unauthorized, a redirect to the
registration page makes sense. But in case of the `NBPWalletController` actions, the
SAML provider and uid are missing and the provided alert message is more meaningful.

Part of XI-6523

Author: nenock

app/controllers/application_controller.rb

@@ -82,6 +82,8 @@ def render_error(message, status) # rubocop:disable Metrics/AbcSize
         if request.url == request.referer || request.referer&.match?(new_user_session_path)
           redirect_to :root, alert: message
         elsif current_user.nil? && status == :unauthorized
+          return redirect_to :root, alert: message if request.path.start_with?('/users/nbp_wallet')
+
           store_location_for(:user, request.fullpath) if current_user.nil?
           redirect_to new_user_session_path, alert: t('common.errors.not_signed_in')
         else