allow using data stack without data_stack_init().
allow using data stack without data_stack_init().

--HG--
branch : HEAD

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