rawissueasset doesn't allow asset_amount of zero while issueasset does

elements 0.18.1.9

rawissueasset doesn't allow asset_amount of zero:
```
Invalid parameter, asset_amount must be positive
```

Whereas this is ok using `issueasset`. If you use `issueasset 0 1` you get zero asset amount and 1 reissuance token and then you can effectively reissue the asset into existence.

Would be good if you could do the same with `rawissueasset` for cases where people want to issue an asset and want to know the asset id but do not know the amount they need yet.

Empieza localizando los puntos de entrada de los comandos o RPC rawissueasset e issueasset y reproduce la diferencia con los ejemplos del issue: un importe de asset igual a cero y un token de reissuance. Comprueba cómo rawissueasset valida asset_amount; se considerará terminado cuando el caso de importe cero se acepte de forma coherente, conservando el ID de asset devuelto y el comportamiento de reissuance.

Escrito por el modelo de indexación a partir del texto del issue.