luanti/mineclonia: attempt to perform arithmetic on a nil value

[helce]

Bug found on luanti run. Reproduces only with jon. Need to reduce test.

test.txt

$ luajit test.lua
luajit: test.lua:17: attempt to perform arithmetic on a nil value
stack traceback:
        test.lua:17: in function 'mul'
        test.lua:38: in main chunk
        [C]: at 0x0001d7f0

$ luajit -joff test.lua
<OK>

[helce]

Fails here:
carry = carry + factor * src1[k] * src2[j + 1 - k]

with k = 2 and j = 1 (should be k = 1 and j = 2)

k = math_max(1, j + 1 - #src2), math_min(j, #src1)

here the problem max(1, 1 + 1 - 2) = 1, min (1, 2) = 1

Short example:

do
  local function mul(src1, src2, result_length)
    local carry = 0.0
    for j = 1, result_length do
      for k = math.max(1, j + 1 - #src2), math.min(j, #src1) do
        print(string.format("k: %d, j: %d\n", k, j))
        carry =  carry + src1[k] * src2[j + 1 - k]
      end
    end
   return carry
 end

  for i=1,50 do
    local src1 = {1234, 4321}
    local src2 = {5678, 8765}
    local res = mul(src1, src2, 2)
  end
end

[helce]

ok, it's my fail, but only in devel