It is possible to create a CTL LUN that is not associated with any
target. For example, prior to 15b3e3bb7efc that could happen if the
user exceeded kern.cam.ctl.max_ports and tried to create an additional
LUN. In this case, report the LUN to Prometheus as having no target at
all, rather than failing the command.
MFC after: 2 weeks
Sponsored by: Axcient