fix frozeWithCacheReuse

[molon]

func Test_customize_map_key_encoder(t *testing.T) {
	should := require.New(t)
	cfg := jsoniter.Config{}.Froze()
	cfg.RegisterExtension(&testMapKeyExtension{})
	m := map[int]int{1: 2}

	b, err := cfg.MarshalIndent(m, "", "  ")
	should.NoError(err)
	should.Equal(`{
  "2": 2
}`, string(b))

	cfg = jsoniter.Config{}.Froze() // without testMapKeyExtension
	b, err = cfg.MarshalIndent(m, "", "  ")
	should.NoError(err)
// !!!!! Before fix, it won't be equal here !!!!!!!
	should.Equal(`{
  "1": 2
}`, string(b))
}