`dd` on line 1 crashes the program.

[JuhaJGamer]

Yeah, an issue for a Minecraft version of vi.

Anyway,

Steps to reproduce

1. Open vi on any CC: Tweaked computer.
2. Enter insert mode, write something on the first line and return to normal mode
3. Write dd

Expected behaviour

The first line should be blanked, returning you to an empty file

Actual behaviour

vi.lua:573: attempt to get length of field '?' (a nil value)
|Line 573
|        if newX > #lines[newY] then
|
> _

I do see that it is marked with TODO: Fix, and I think the time may be approaching when the number of users (approximately 1) has risen so high that the application may require maintenance again.

Non-expert diagnosis

You're deleting the line. That's fine, unless we're on the first line, in which case setCursor tries to read the length of that line. lines should be used safely if it can ever be empty, or unsafely only if it is guaranteed to never be. I've personally taken the liberty of defining

local function removeLine(lineY)
    table.remove(lines,lineY)
    if #lines == 0 then
        table.insert(lines, "")
    end
end

and replaced each table.remove(lines,y) with it. This seems to have largely repaired the issue.