MMS: Handle case when mobile data is not available

mmsNetworkInfo is null on devices without a modem where mobile data is not available
causing a null pointer crash

CRs-Fixed: 517339

Change-Id: I2522d9da3cea1599d7b865e12134b508b636bde9
(cherry picked from commit eae5bd0bad88c16b98a353eccd66dd38e26b3b97)
(cherry picked from commit f6f5777a6e8f5edee1befe45aa8a69c4447b4dbd)
(cherry picked from commit ed1560a24deeaf4df8034b1851a1c4afe2a30d9c)