ext_offsets can be higher than int_offsets, so check its validity instead before starting syncing.
ext_offsets can be higher than int_offsets, so check its validity instead
before starting syncing.

--HG--
branch : HEAD

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