Exception in subscription body fails key registration

[arv]

If we get an exception when a subscription body is called then we do not know what keys it depends on and we fail to call it again when we the keys change.

For example:

rep.subscribe(
  async tx => {
    const a = await tx.get('a');
    if (!a) {
      throw new Error('oops');
    }
    return a;
  },
  {
    onDone(result) {},
    onError(error) {
      console.error(error);
    },
  },
);

Thanks @aroc for helping us find this.