AttributeError: Debugger instance has no attribute 'bend'

After some fooling around with

:Dbg b
(timeout)
:Dbg quit
:Dbg -
(timeout)
:Dbg quit
:Dbg .

I got an error message that I dismissed by accident without being able to read. Now I cannot :Dbg quit -- I get this traceback:

```
Traceback (most recent call last):
File "", line 1, in
File "/home/mg/.vim/plugin/vim_debug/commands.py", line 44, in debugger_cmd
cmd['function'](*args)
File "/home/mg/.vim/plugin/vim_debug/new_debugger.py", line 187, in quit
self.bend.close()
AttributeError: Debugger instance has no attribute 'bend'
```

":Dbg ." now doesn't work either -- prints the usage message -- so there's no obvious way to debug anything without restarting vim.

從 new_debugger.py 中 quit 處的 traceback 以及 commands.py 中 debugger_cmd 處的命令分派開始。重現列出的 :Dbg 序列，然後追蹤偵錯器狀態的建立與關閉方式；當 :Dbg quit 和 :Dbg . 不需重新啟動 Vim 即可再次正常運作時，就算完成。

由索引模型根據 Issue 內容生成。