Fix json5 downgrade with dangling comma (#21)

json5/json5.go

@@ -32,7 +32,17 @@ func Downgrade(data []byte) ([]byte, error) {
 		return nil, err
 	}
 
-	return json.Marshal(v)
+	if d, err := json.Marshal(v); err == nil {
+		return d, nil
+	}
+
+	// Fallback decoding for cases like a dangling comma.
+	var i interface{}
+	if err := Unmarshal(data, &i); err != nil {
+		return nil, err
+	}
+
+	return json.Marshal(i)
 }
 
 // Unmarshal parses the JSON5-encoded data and stores the result

json5/json5_test.go

@@ -56,6 +56,18 @@ func TestDowngrade(t *testing.T) {
 	assert.Equal(t, `{"xyz":123,"abc":987}`, string(j))
 }
 
+func TestDowngrade2(t *testing.T) {
+	dd, err := json5.Downgrade([]byte(`{
+  "values": {
+    "app_token::$appToken::web_tracking_enabled": "1",
+    "app_token::$appToken::web_redirect_base_url": "http://redirect.com",
+  }
+}`))
+
+	require.NoError(t, err)
+	assert.Equal(t, `{"values":{"app_token::$appToken::web_redirect_base_url":"http://redirect.com","app_token::$appToken::web_tracking_enabled":"1"}}`, string(dd))
+}
+
 func TestDowngrade_array(t *testing.T) {
 	j5 := `		[{
 		// XYZ.