[Settings] DataUsage crash when no SIM inserted

Check for null pointer when looking up subcription id.

Bug: 148175728
Test: m RunSettingsRoboTests -j ROBOTEST_FILTER=DataUsageUtilsTest
Change-Id: Icc1314d262f1af686134dcf6a0b187adfc3eb4df
Merged-In: I4e893fc7de4a3292b3949860ebb59fbe52ac1a8f
1 file changed