Don't resort empty plugins alphabetically

[Silarn]

After packing some loose file mods and creating empty light plugins to load the archives, I've discovered that running the sorter seems to reorder these plugins alphabetically.

I think it makes more sense to preserve the existing load order of such ambiguously sorted plugins so that it doesn't potentially break what might be an intentional archive load order.

[Ortham]

LOOT already uses existing load order, but if they were new plugins then they might not have had load order positions yet, in which case it falls back to comparing filenames.

[Silarn]

This is not what I'm experiencing, though it is with Starfield which may be part of the problem. I have a number of dummy light plugins set up to load archives and these seem to be sorting alphabetically every time I run the sort.

[Ortham]

Sorting Starfield load orders is effectively broken unless Bethesda make changes, and disabled in the latest snapshot builds, so I don't think there's any point debugging the issue at this time.