Don't delete DH params if they aren't created

src/freedombone-clientcert

 
 # move the cert to the user's home
 mkdir /home/$USERNAME/emailcert
-shred -zu /etc/ssl/certs/$USERNAME.dhparam
 mv /etc/ssl/certs/$USERNAME.cer /home/$USERNAME/emailcert
 cp /etc/ssl/certs/dovecot-ca.crt /home/$USERNAME/emailcert
 mv /etc/ssl/private/$USERNAME.key /home/$USERNAME/emailcert