cronjob that deletes quarantined mails

==== Required information ====
- iRedMail version: 0.8.5
- Store mail accounts in which backend (LDAP/MySQL/PGSQL): mysql
- Linux/BSD distribution name and version: Debian 7.3
- Related log if you're reporting an issue:
====
Hi,

i noticed the following problem with the cronjob that deletes the quarantined mails older than 15 days.

crontab of user amavis
# Delete virus mails which created 15 days ago.
1   5   *   *   *   find /var/lib/amavis/virusmails/ -ctime +15 | xargs rm -rf {}

If i receive no infected mail for more than 15 days the cronjob also deleted the directory /var/lib/amavis/virusmails/.
After this quarantined mails are stored in a single file /var/lib/amavis/virusmails and not in a directory. And the cronjob results with an error that the directory does not exist.

My solution/workaround:
Because it is easier to change the modify date i do a touch on the directory first. And i use -mtime instead of -ctime.

# Delete virus mails which created 15 days ago.
1   5   *   *   *   touch /var/lib/amavis/virusmails ; find /var/lib/amavis/virusmails/ -mtime +15 | xargs rm -rf {}

Cheers,
Stefan