Ensure AR #second, #third, etc. finders work through associations

This commit fixes two regressions introduced in cafe31a078 where
newly created finder methods #second, #third, #forth, and #fifth
caused a NoMethodError error on reload associations and where we
were pulling the wrong element out of cached associations.

Examples:

  some_book.authors.reload.second

  # Before
  # => NoMethodError: undefined method 'first' for nil:NilClass

  # After
  # => #<Author id: 2, name: "Sally Second", ...>

  some_book.first.authors.first
  some_book.first.authors.second

  # Before
  # => #<Author id: 1, name: "Freddy First", ...>
  # => #<Author id: 1, name: "Freddy First", ...>

  # After
  # => #<Author id: 1, name: "Freddy First", ...>
  # => #<Author id: 2, name: "Sally Second", ...>

Fixes #13783.

1 files changed, 2 insertions, 2 deletions

diff --git a/activerecord/test/cases/inheritance_test.rb b/activerecord/test/cases/inheritance_test.rb
index d2b5a06b55..e2ff2aa451 100644
--- a/activerecord/test/cases/inheritance_test.rb
+++ b/activerecord/test/cases/inheritance_test.rb
@@ -222,9 +222,9 @@ class InheritanceTest < ActiveRecord::TestCase
   end
 
   def test_inheritance_condition
-    assert_equal 10, Company.count
+    assert_equal 11, Company.count
     assert_equal 2, Firm.count
-    assert_equal 4, Client.count
+    assert_equal 5, Client.count
   end
 
   def test_alt_inheritance_condition