maildir: Code cleanup: Use MAILDIR_UIDLIST_HDR_EXT_* when building the header string.
maildir: Code cleanup: Use MAILDIR_UIDLIST_HDR_EXT_* when building the header string.

LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot,LTD-Beget/dovecot