If namespace has a prefix and inbox=no, don't list prefix.inbox if it happens to exist when listing for %.
If namespace has a prefix and inbox=no, don't list prefix.inbox if it
happens to exist when listing for %.

--HG--
branch : HEAD

jwm/dovecot-notmuch,dscho/dovecot,jkerihuel/dovecot,jkerihuel/dovecot,dscho/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,dscho/dovecot,jwm/dovecot-notmuch,jwm/dovecot-notmuch,jkerihuel/dovecot,dscho/dovecot,jkerihuel/dovecot,dscho/dovecot