完善关联统计 避免一对一关联报错

library/think/model/relation/MorphTo.php

@@ -136,6 +136,16 @@ class MorphTo extends Relation
         $this->eagerlyMorphToOne($model, $relation, $result, $subRelation);
     }
 
+    /**
+     * 关联统计
+     * @access public
+     * @param Model     $result 数据对象
+     * @param \Closure  $closure 闭包
+     * @return integer
+     */
+    public function relationCount($result, $closure)
+    {}
+
     /**
      * 多态MorphTo 关联模型预查询
      * @access public