[Dovecot] dovecot-metadata-plugin v14 patches

Please apply patches for dovecot-metadata-plugin v14.

1. dovecot-metadata-plugin-value_nil - fix plugin crach if entry->value == NULL (strlen(NULL) - segfault).
2. dovecot-metadata-plugin-utf7_support - add support metadata for UTF8 mailfolder.

-- Sidlyarenko Sergey https://github.com/lefoyer