istream-seekable: Don't crash when seeking forwards past the data we haven't read yet.
istream-seekable: Don't crash when seeking forwards past the data we haven't read yet.

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