usr.sbin/sesutil: locate all off does not deactivate empty slots

[allanjude]

Summary

Reported By: asomers
PR: 217409

"sesutil locate all off" will skip empty slots. This is a problem, because for example if you use "sesutil locate da5 on" to locate a bad drive and then remove it, you can't turn the beacon off without using a sesid. The fault command is probably affected too, but I didn't test it.

[asomers]

Works for me.