Fix bugs around unification when no password is set

- When in a unified state, selecting the work lock to be "none" caused
a security exception
- When the work lock was set to "none", unifying didn't work
- When in a unified state, the work lock type selection screen showed
"none" as the current type instead of the device lock type

Bug: 26577247
Change-Id: I853d77186e23b6a458eaa6c1047942a7eefddc9c