Flyweight construction issue with empty slots definition

[davidmclifton]

If providing a flyweight constructor expression, if an empty set of slots is provided it throws an error - yet leaving it out provides a flyweight with no slots. Generally in MOO the convention is that optional args go at the end, vs having overrides based on number of args that don't include the earlier args.

> ;<#107, [], {"testing 1"}>;
Failure to parse program @ 1/47: expected ident
47 errors.
> ;<#107, [blah -> "blah"], {"testing 1"}>;
=> <#107, [blah -> "blah"], {"testing 1"}>
> ;<#107, {"testing 1"}>;
=> <#107, {"testing 1"}>