改进model类save方法对字段的判断

library/think/Model.php

@@ -631,9 +631,8 @@ abstract class Model implements \JsonSerializable, \ArrayAccess
 
         // 检测字段
         if (!empty($this->field)) {
-            $this->db();
             foreach ($this->data as $key => $val) {
-                if (!in_array($key, $this->field)) {
+                if (!in_array($key, $this->field) && !array_key_exists($key, $this->field)) {
                     unset($this->data[$key]);
                 }
             }