Make sure Bundle#ends_at is set before validation

otherwise we risk creating overlapping bundles and not catching it.

app/models/notification/bundle.rb

@@ -15,7 +15,7 @@ class Notification::Bundle < ApplicationRecord
     )
   end
 
-  before_create :set_default_window
+  before_validation :set_default_window, if: :new_record?
 
   validate :validate_no_overlapping
 

test/models/notification/bundle_test.rb

@@ -83,6 +83,16 @@ class Notification::BundleTest < ActiveSupport::TestCase
     assert bundle_5.valid?
   end
 
+  test "overlapping bundles that are created relying on set_default_window are not created" do
+    @user.notification_bundles.destroy_all
+
+    bundle = @user.notification_bundles.create!(starts_at: Time.current)
+
+    assert_raises ActiveRecord::RecordInvalid do
+      @user.notification_bundles.create!(starts_at: bundle.starts_at - 1.second)
+    end
+  end
+
   test "deliver_all delivers due bundles" do
     notification = @user.notifications.create!(source: events(:logo_published), creator: @user)