修复skn传值为空时会清除所有浏览记录的bug

Code Review By Rock Zhang

@@ -359,13 +359,19 @@ class UserModel
     {
         $result = array('code' => 400, 'message' => '出错啦~');
 
-        $record = UserData::delRecord($uid, $skn);
+        do {
+            if (empty($skn)) {
+                break;
+            }
 
-        // 处理数据
-        if ($record && isset($record['code'])) {
-            $result['code'] = $record['code'];
-            $result['message'] = $record['message'];
-        }
+            $record = UserData::delRecord($uid, $skn);
+
+            // 处理数据
+            if ($record && isset($record['code'])) {
+                $result['code'] = $record['code'];
+                $result['message'] = $record['message'];
+            }
+        } while (false);
 
         return $result;
     }