Check that mDrivingStateManager is not null.

bug: 117220307
Test: m and install
Change-Id: I1bcfbe5075dee4ab2fb77c22e98992ce548ed970
(cherry picked from commit 015dd425c2dc626d8806be2bac6e7d927648c126)

packages/CarSystemUI/src/com/android/systemui/statusbar/car/DrivingStateHelper.java

@@ -52,6 +52,9 @@ public class DrivingStateHelper {
      * is idling or moving, {@code false} otherwise.
      */
     public boolean isCurrentlyDriving() {
+        if (mDrivingStateManager == null) {
+            return false;
+        }
         try {
             CarDrivingStateEvent currentState = mDrivingStateManager.getCurrentCarDrivingState();
             if (currentState != null) {