swapongeom: destroy consumer/close vnode in case swaponsomething failed
Fixes: aa42e4984997c9d3aa5d30534bdaf760e613e97b
Reported and tested by: olivier
Reviewed by: alc, markj
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D51636