fix: 解决shell命令中rm -r指令尝试删除/dev下节点系统出错的问题

主干不存在该问题，已解决.

shell命令rm中当opendir时没有正确判断opendir的返回值,
导致后续访问空指针.

检查opendir的返回值,当opendir失败时返回-1.

Close #I48FLX

Signed-off-by: gao-rongxin <gaorongxin1@huawei.com>

fs/vfs/vfs_cmd/vfs_shellcmd.c

@@ -838,6 +838,10 @@ static int os_shell_cmd_do_rmdir(const char *pathname)
       return remove(pathname);
     }
   d = opendir(pathname);
+    if (d == NULL)
+    {
+        return -1;
+    }
   while (1)
     {
       dirent = readdir(d);