Disable "lock keyring" if no passphrase has been set

[diracdeltas]

dougdeperry:

The UI should not let allow you to “Lock keyring” if you do not have a passphrase already set. Maybe
attempting this action should take you to the "create a passphrase" workflow?

dgil:

Actually, this could be reasonably sensible, given how things work right now. It's possible to create a
non-extractable wrapping key, and then encrypt before serializing to localStorage via a shim.

(This may or may not be useful in the least, but for exactly the same reasons passwords may not be
very useful.)