hang/crash when closing last pane in tab with hidden floating pane

[tlinford]

zellij --version: 0.27.0

When there is a hidden floating pane, and one closes all other panes so that the current tab would close, zellij hangs, and subsequent keypresses cause a crash.

Steps to reproduce:

1. Open floating pane
2. Focus existing tiled pane
3. Press ctrl+d or close pane with keybindings
4. At this point everything is stuck, press any key and it will crash with:

Error occurred in server:

  × Thread 'screen' panicked.
  ├─▶ Originating Thread(s)
  │   	1. stdin_handler_thread: AcceptInput
  │   	2. screen_thread: WriteCharacter
  │
  ├─▶ At zellij-server/src/tab/mod.rs:822:60
  ╰─▶ called `Option::unwrap()` on a `None` value

This happens after #1239.

[imsnif]

Honestly, I'm wondering what the correct behaviour here should be. We can fix the crash as before, but what'll happen is that the floating pane will be unceremoniously closed without any indication to the user. What would you expect here?

[tlinford]

Good question - the previous behavior seemed mostly sensible to me, but I can see that might be surprising in some cases.