Simultaneous ssh with ProxyJump causes crash

When using `ssh` to access a host behind a configured `ProxyJump` host, a-shell will crash when a second connection (in another window) is opened to the same host. This also happens if a `ProxyCommand` is configured for the destination — resulting in a segmentation fault.

To reproduce, simply add a host configuration with `ProxyJump` to `~/.ssh/config`:
```
Host example.com
ProxyJump jump.example.com
```
Then `ssh` to `example.com`. Open a second window and `ssh` to `example.com`. Both shells will crash.