Subnautica: fix use of _valid_keys were valid_keys should be used. (#3346)

* Subnautica: fix use of _valid_keys were valid_keys should be used.

* Update Options.py

Options.py

@@ -746,6 +746,7 @@ class NamedRange(Range):
 
 class FreezeValidKeys(AssembleOptions):
     def __new__(mcs, name, bases, attrs):
+        assert not "_valid_keys" in attrs, "'_valid_keys' gets set by FreezeValidKeys, define 'valid_keys' instead."
         if "valid_keys" in attrs:
             attrs["_valid_keys"] = frozenset(attrs["valid_keys"])
         return super(FreezeValidKeys, mcs).__new__(mcs, name, bases, attrs)