We can exit very soon if we enter a visitor with a preexisting error.
This simplifies some cases because we will not have to deal with
obj being non-NULL while *obj is NULL.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Reviewed-by: NAnthony Liguori <aliguori@us.ibm.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>