fix: fix objects with bogus prototypes

Fix #130 This seems likely to be thrown by this line: https://github.com/nolanlawson/fuite/blob/40825977886e1e0cfa85a5ce575652fc1d07328e/src/metrics/collections/collections.js#L39 If `ctor` is null then we would throw. We should also check for oddballs like a `get constructor()` that throws.