fix https://gitee.com/baomidou/mybatis-plus/issues/I3T0LA

mybatis-plus-extension/src/main/kotlin/com/baomidou/mybatisplus/extension/kotlin/KtQueryChainWrapper.kt

@@ -27,7 +27,7 @@ import kotlin.reflect.KProperty
  * @author FlyInWind
  * @since 2020-10-18
  */
-class KtQueryChainWrapper<T : Any>(
+open class KtQueryChainWrapper<T : Any>(
     internal val baseMapper: BaseMapper<T>
 ) : AbstractChainWrapper<T, KProperty<*>, KtQueryChainWrapper<T>, KtQueryWrapper<T>>(),
     ChainQuery<T>, Query<KtQueryChainWrapper<T>, T, KProperty<*>> {

mybatis-plus-extension/src/main/kotlin/com/baomidou/mybatisplus/extension/kotlin/KtUpdateChainWrapper.kt

@@ -25,7 +25,7 @@ import kotlin.reflect.KProperty
  * @author FlyInWind
  * @since 2020-10-18
  */
-class KtUpdateChainWrapper<T : Any>(
+open class KtUpdateChainWrapper<T : Any>(
     internal val baseMapper: BaseMapper<T>
 ) : AbstractChainWrapper<T, KProperty<*>, KtUpdateChainWrapper<T>, KtUpdateWrapper<T>>(),
     ChainUpdate<T>, Update<KtUpdateChainWrapper<T>, KProperty<*>> {