Fix data icon issue for null apn

When data call is setup on null apn, data
connection state is notified as suspended
as Telephony is treating null apn as provisioning
apn. This is because the xml entry for
provisioning apn is empty which is matching
empty apn name.
Add isEmpty check for provisioning apn xml entry

Change-Id: Ifbb3aaaf18926b9209aa05f8346da839178dc803
CRs-Fixed: 713896