修复了Task在update时如果完全没有改动会报错的问题

src/main/java/cn/edu/hfut/rmdjzz/projectmanagement/controller/TaskController.java

@@ -82,6 +82,7 @@ public class TaskController {
             throw new BadRequestException(IProjectService.PROJECT_UNOPENED);
         task.setTaskProjectId(projectId);
         task.setTaskId(taskId);
+        task.setDeleted(false);
         taskService.modifyTask(token, task);
         return ResponseMap.ofSuccess();
     }