KDL layouts: problematic percentage sizes

[raphCode]

version: main, roughly 12d35bd

There are some relative sizes that can cause trouble:

Small sizes: 0% - (100/number of terminal lines)%

layout {
    pane size="0%"
    pane
}

Upon loading this layout I get either:

• Bye from zellij!
• Garbage from the sixel image palette stuff (Probably the terminal emulator sending its response into my shell prompt)

log shows:

ERROR  |zellij_server::tab       | 2022-10-19 16:34:04.125 [screen    ] [zellij-server/src/tab/mod.rs:609]: No room on screen for this layout!
INFO   |zellij_client            | 2022-10-19 16:34:04.125 [main      ] [zellij-client/src/lib.rs:393]: Bye from Zellij!
INFO   |zellij_server::wasm_vm   | 2022-10-19 16:34:04.129 [wasm      ] [zellij-server/src/wasm_vm.rs:213]: wasm main thread exits
ERROR  |zellij_utils::errors::not| 2022-10-19 16:34:04.129 [async-std/runti] [zellij-utils/src/errors.rs:435]: Panic occured:
             thread: async-std/runtime
             location: At zellij-server/src/terminal_bytes.rs:124:14
             message: called `Result::unwrap()` on an `Err` value: failed to send message to screen

This also happens with size=0

Sizes summing > 100%

layout {
    pane size="50%"
    pane size="50%"
    pane size="50%"
}

This opens zellij, but the last pane is only 1 line tall, and also resizing is kinda broken: The upper panes keep their original size if they still have vertical space. The first pane that exceeds the window height is resized, but fails to display its bottom pane frame:

When the window gets bigger, the extra space is not filled at all:

With four panes of size 50% I can even get a server crash if I try to close them (similar symptoms like #1821)

[imsnif]

I'm issuing a fix for the 0% case. The other issue has been with us for a while and will require a much needed overhaul to our resizing system. The latter will also fix all the fixed pane issues. For now I'm afraid we're going to have to trust users on this one.