分块上传错误时，无法删除已经合并的分块文件

Signed-off-by: 渲染 <pay@ktwap.net>

application/common/library/Upload.php

@@ -305,7 +305,7 @@ class Upload
 
             $attachment = $this->upload();
         } catch (\Exception $e) {
-            @unlink($destFile);
+            is_file($uploadPath) && @unlink($uploadPath);
             throw new UploadException($e->getMessage());
         }
         return $attachment;