Providing callback function to findShortestPathBetween crashes the server

As in the title. Providing callback to `findShortestPathBetween` function crashes the server without any errors.

```lua
local id = loadPathGraph('nodes.json')

if isGraphLoaded(id) then
    iprint('Loaded graph with id: ',id)

    findShortestPathBetween(id,0,0,0,100,100,100,function(nodes)
        iprint('callback')
    end)
end

unloadPathGraph(id)
```