migration: Check that postcopy fd's are not NULL
If postcopy has finished, it frees the array. But vhost-user unregister it at cleanup time.
fixes: c4f75385 Signed-off-by: Juan Quintela quintela@redhat.com Reviewed-by: Dr. David Alan Gilbert dgilbert@redhat.com (cherry picked from commit 56559980)
Bugzilla: bz1982224
Brew: 41123115
Signed-off-by: Juan Quintela quintela@redhat.com