Allow ostruct to return a value on super (#4028)

This fixes cases where you can super in something that inherits from OpenStruct

Co-authored-by: John Hawthorn <john@hawthorn.email>

lib/ostruct.rb

@@ -250,6 +250,7 @@ def freeze
       end
       set_ostruct_member_value!(mname, args[0])
     elsif len == 0
+      @table[mid]
     else
       begin
         super

test/ostruct/test_ostruct.rb

@@ -246,6 +246,14 @@ def test_overriden_private_methods
     assert_equal(:bar, os.format)
   end
 
+  def test_super
+    c = Class.new(OpenStruct) {
+      def foo; super; end
+    }
+    os = c.new(foo: :bar)
+    assert_equal(:bar, os.foo)
+  end
+
   def test_overridden_public_methods
     os = OpenStruct.new(method: :foo, class: :bar)
     assert_equal(:foo, os.method)