ZodFastCheck().outputOf(z.record(z.number(), z.number())) only builds empty records

This test passes:

```
it('only builds empty records', () => {
fc.assert(
fc.property(
ZodFastCheck().outputOf(z.record(z.number(), z.number())),
(xs) => {
assert(Object.keys(xs).length === 0);
},
),
);
});
```

But it would be great if it failed.

Start by reproducing the shown test for ZodFastCheck().outputOf(z.record(z.number(), z.number())). Trace the record-schema handling from that entry point and identify why generated objects are always empty. Done means the property no longer passes because generated records can contain entries while still satisfying the schema.

Written by the indexing model from the issue text.