lib-storage: Removed unnecessary code. mailbox_dir_name is never NULL, and when it's empty it can be handled exactly the same as when it's non-empty.
lib-storage: Removed unnecessary code.
mailbox_dir_name is never NULL, and when it's empty it can be handled
exactly the same as when it's non-empty.

dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot,dscho/dovecot