Telephony: check if the provisioning apn is actually empty before

checking if they are equal.  Fixes cases where the stubbed apn
(empty) equal to the empty provisioning apn.

Fixes no IP issues on CDMA data types.

Change-Id: Id7bda83778f5ce59c87463c4d44fc5768dbc4a08
fix for Samsung CDMA incoming SMS bug

ported from CM7/9/10

requires: http://review.cyanogenmod.org/#/c/26917/

Change-Id: I6189dd0c6aeffb0b8b530bab7994a07bb390c32c