ProjectMoved#add_redirect_message does not handle anonymous clones

https://sentry.gitlap.com/gitlab/gitlabcom/issues/115616/

NoMethodError: undefined method `id' for nil:NilClass
  lib/gitlab/checks/project_moved.rb:25:in `block in add_redirect_message'
    key = self.class.redirect_message_key(user.id, project.id)
  lib/gitlab/redis/wrapper.rb:17:in `block in with'
    @pool.with { |redis| yield redis }
  lib/gitlab/redis/wrapper.rb:17:in `with'
    @pool.with { |redis| yield redis }
  lib/gitlab/checks/project_moved.rb:24:in `add_redirect_message'
    Gitlab::Redis::SharedState.with do |redis|
  lib/gitlab/metrics/instrumentation.rb:159:in `block in add_redirect_message'
    .measure { super }
...
(130 additional frame(s) were not displayed)

NoMethodError: undefined method `id' for nil:NilClass