[BUG] usePreset() makes API call when scratch.preset is undefined

[Mark Street]

Describe the bug
We shouldn't make an API call if the value of the preset id is undefined. This results in an error in the client's console, as well as a warning in the server logs:

GET https://decomp.me/api/preset/undefined 404 (Not Found)

To Reproduce
Steps to reproduce the behavior:

1. Go to any Scratch with a preset
2. Click on Options
3. Change the Compiler (e.g from ido5.3 to ido7.1, anything to result in a Custom preset)
4. See error message in browser's dev console

Expected behavior
I don't expect the API call to be made when we know we have an invalid preset

[Alex Bates]

possible solution: https://discord.com/channels/897066363951128586/897075447534354462/1187046605006831636

export function usePreset(id: number | undefined): Preset | undefined {
    const url = typeof id === "number" ? `/preset/${id}` : null
    const { data } = useSWR(url, get, {
        refreshInterval: 0,
        onErrorRetry,
    })
    return data
}