Fix NoMethodError when cookies == :none

When tracking with no visit,

```
Ahoy.cookies = :none
Ahoy::Tracker.new.track_event(:would_fail)
```

would raise NoMethodError: undefined method `remote_ip' for nil.
Since we explicitly don't have a request, allow visitor_token_helper
to fall back on generate_id by not calling visitor_anonymity_set when
there is no request.

lib/ahoy/tracker.rb

@@ -241,7 +241,9 @@ def existing_visitor_token
     end
 
     def visitor_anonymity_set
-      @visitor_anonymity_set ||= Digest::UUID.uuid_v5(UUID_NAMESPACE, ["visitor", Ahoy.mask_ip(request.remote_ip), request.user_agent].join("/"))
+      @visitor_anonymity_set ||= Digest::UUID.uuid_v5(
+        UUID_NAMESPACE, ["visitor", Ahoy.mask_ip(request.remote_ip), request.user_agent].join("/")
+      ) if request
     end
 
     def visit_cookie

test/tracker_test.rb

@@ -11,6 +11,21 @@ def test_no_request
     assert_nil event.user_id
   end
 
+  def test_no_request_with_cookies_none
+    old_cookies = Ahoy.cookies
+    Ahoy.cookies = :none
+
+    ahoy = Ahoy::Tracker.new
+    ahoy.track("Some event", some_prop: true)
+
+    event = Ahoy::Event.last
+    assert_equal "Some event", event.name
+    assert_equal({"some_prop" => true}, event.properties)
+    assert_nil event.user_id
+  ensure
+    Ahoy.cookies = old_cookies
+  end
+
   def test_no_cookies
     request = ActionDispatch::TestRequest.create