Fix null handling of getAllCellInfo

ServiceStateTracker.getAllCellInfo may return null, but
PhoneBase.privatizeCellInfoList may dereference that.  Check
for null rather than crash the phone.

bug:23201508
Change-Id: I26fcfc015fa1a8d1ec13e34f3369d1848954c44e
diff --git a/src/java/com/android/internal/telephony/PhoneBase.java b/src/java/com/android/internal/telephony/PhoneBase.java
index 570f863..4037392 100644
--- a/src/java/com/android/internal/telephony/PhoneBase.java
+++ b/src/java/com/android/internal/telephony/PhoneBase.java
@@ -1314,6 +1314,7 @@
      * @return the original list with CDMA lat/long cleared if necessary
      */
     private List<CellInfo> privatizeCellInfoList(List<CellInfo> cellInfoList) {
+        if (cellInfoList == null) return null;
         int mode = Settings.Secure.getInt(getContext().getContentResolver(),
                 Settings.Secure.LOCATION_MODE, Settings.Secure.LOCATION_MODE_OFF);
         if (mode == Settings.Secure.LOCATION_MODE_OFF) {