fix BufWinLeave for the main Vdebug windows
fix BufWinLeave for the main Vdebug windows

Avoids trace:
```
Error detected while processing BufWinLeave Autocommands for "DebuggerBreakpoints":
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/home/user/.vim/pack/bundle/opt/vdebug/python3/vdebug/debugger_interface.py", line 114, in mark_window_as_closed
    self.session_handler.ui().mark_window_as_closed(window)
  File "/home/user/.vim/pack/bundle/opt/vdebug/python3/vdebug/ui/vimui.py", line 173, in mark_window_as_closed
    self.windows.window(name).mark_as_closed()
  File "/home/user/.vim/pack/bundle/opt/vdebug/python3/vdebug/ui/vimui.py", line 533, in mark_as_closed
    self.destroy()
  File "/home/user/.vim/pack/bundle/opt/vdebug/python3/vdebug/ui/vimui.py", line 598, in destroy
    vim.command('bwipeout %s' % self.name)
vim.error: Vim(bwipeout):E937: Attempt to delete a buffer that is in use: DebuggerBreakpoints
```

fixes: #451

Signed-off-by: BlackEagle <6c5c99a37e4dd8841971a4b7c7580d6fcba68554@gmail.com>

joonty/vdebug,paprykarz/vdebug,paprykarz/vdebug,paprykarz/vdebug,joonty/vdebug,joonty/vdebug