Add back loading definitions in after_initialize

We removed the call to `FactoryBot.load_definitions` in the
`after_initialize` hook in dcfc9f6 because the other changes in that
commit were causing us to sometimes call `FactoryBot.load_definitions`
after `FactoryBot.reload`.

We could have changed `FactoryBot.load_definitions` to
`FactoryBot.reload`, which is what this PR does, but it didn't seem
necessary at the time since all the tests were still passing.

We fixed a problem in 9b83f48 that was causing us to watch the root
directory of the project. This fix caused a test failure, but I ended up
changing the test in 2b7bca0 because it seemed like an unlikely
scenario.

This PR adds back the original test case. Although I do think it
unlikely, I would rather not risk making a breaking change in the next
patch release.

features/load_definitions.feature

@@ -115,7 +115,44 @@ Feature: automatically load factory definitions
     When I run `bundle exec rake test` with a clean environment
     Then the output should contain "1 assertions, 0 failures, 0 errors"
 
-  Scenario: use 3rd-party factories with an initializer
+  Scenario: use 3rd-party factories with an initializer and without any user-defined factories
+    When I append to "config/application.rb" with:
+      """
+        require File.expand_path('../../lib/some_railtie/railties.rb', __FILE__)
+      """
+    When I write to "lib/some_railtie/railties.rb" with:
+      """
+      module SomeRailtie
+        class Railtie < ::Rails::Engine
+          initializer "some_railtie.factories", :after => "factory_bot.set_factory_paths" do
+            FactoryBot.definition_file_paths << File.expand_path('../factories', __FILE__)
+          end
+        end
+      end
+      """
+    When I write to "lib/some_railtie/factories.rb" with:
+      """
+      FactoryBot.define do
+        factory :factory_from_some_railtie, class: 'User' do
+          name { 'Artem' }
+        end
+      end
+      """
+    When I write to "test/unit/user_test.rb" with:
+      """
+      require 'test_helper'
+
+      class UserTest < ActiveSupport::TestCase
+        test "use factory of some_railtie" do
+          railtie_user = FactoryBot.create(:factory_from_some_railtie)
+          assert_equal 'Artem', railtie_user.name
+        end
+      end
+      """
+    When I run `bundle exec rake test` with a clean environment
+    Then the output should contain "1 assertions, 0 failures, 0 errors"
+
+  Scenario: use 3rd-party factories with an initializer together with a user-defined factory
     When I append to "config/application.rb" with:
       """
         require File.expand_path('../../lib/some_railtie/railties.rb', __FILE__)

lib/factory_bot_rails/railtie.rb

@@ -22,6 +22,10 @@ module FactoryBotRails
       Reloader.new(app, config).run
     end
 
+    config.after_initialize do
+      FactoryBot.reload
+    end
+
     private
 
     def definition_file_paths