[FIX] SMODS.is_eternal does not properly work for objects without a default eternal_compat value

[the-Astra]

This is a small change that prevents SMODS.is_eternal for falsely assuming incompatibility for objects without a default eternal_compat value

Additional Info:

• I didn't modify api's or I've made a PR to the wiki repo.
• I didn't modify api's or I've updated lsp definitions.
• I didn't make new lovely files or all new lovely files have appropriate priority.