imap-zlib: Fixed crash if imap_zlib_compress_level setting wasn't set.
imap-zlib: Fixed crash if imap_zlib_compress_level setting wasn't set.

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branch : HEAD

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