[BUG] the whole software hangs after the serial device unpluged.

### Env

- ubuntu20.04
- windterm2.4.1

### steps

1. open windterm
2. open a remote ssh
3. open a local bash
4. plug the nucleo stm32f767zi board to the usb
5. open the serial communication window with custom port `/dev/serial/by-id/usb-STMicroelectronics_STM32_STLink_0670FF555071494867152654-if02`
6. unplug the board
7. the serial window shows no resource available
8. the whole window no response
9. forcequit the windterm

### aditional info

putty command is

```sh
putty /dev/serial/by-id/usb-STMicroelectronics_STM32_STLink_0670FF555071494867152654-if02 -serial -sercfg 115200,8,n,1,N
```

thanks!

Reproduce the issue in the serial communication window on Ubuntu 20.04 using the listed STM32 device path, then unplug the board while an SSH and local bash session are open. Trace the serial-device disconnect handling and verify that the window remains responsive after the resource becomes unavailable.

Written by the indexing model from the issue text.