sms_queue: Print dest msisdn instead of unknown subscriber

If subscriber is NULL, vlr_subscr_msisdn_or_name() returns string
"unknown", which is less informative than printing destination msisdn
expected for the queued sms.
This happens for instance if an sms was queued with Store&Forward and
destination subscriber is not currently registered

Change-Id: I4b8b54c9c41b17d4e1fa7ece63aa91a98036ef11
1 file changed