Panic on KDL layout file with pane template and children

[raphCode]

#1759

I tried to convert my layout file utilizing the pane templates but managed to crash zellij on startup. I am currently not sure if my kdl is invalid, but if that would be the case, I expected an error message.

Minimal repro:

layout {
    pane_template name="aaa" {
        command "bash"
        children
    }
    aaa
}

thread 'main' panicked at 'insertion index (is 1) should be <= len (is 0)', library/alloc/src/vec/mod.rs:1345:13

Some things I tried:

• Removing children works
• Inserting child panes does not work
• Doing both of the previous at the same time yields a KDL error message that tells me to insert a children block in the template, which is exactly how I was guided towards this bug.