Fix a NPE in BatteryStatsImpl

ServiceManager.getService("batteryproperties")) may return null for some
devices right after boot. (We don't know why, need further investigation)
This causes async batterystats update to crash, leaving BatteryStats in a
bad state (OnBattery() == true, but mOnBatteryTimeBase is not running),
which does not accept aggregated stats update anymore.

Bug: 109930230
Test: manual
Change-Id: I0654beff95f0a2b9df2567f1a2efffd3330e58ff
diff --git a/core/java/com/android/internal/os/BatteryStatsImpl.java b/core/java/com/android/internal/os/BatteryStatsImpl.java
index d7db2e2..5b83799 100644
--- a/core/java/com/android/internal/os/BatteryStatsImpl.java
+++ b/core/java/com/android/internal/os/BatteryStatsImpl.java
@@ -4021,7 +4021,9 @@
         try {
             IBatteryPropertiesRegistrar registrar = IBatteryPropertiesRegistrar.Stub.asInterface(
                     ServiceManager.getService("batteryproperties"));
-            registrar.scheduleUpdate();
+            if (registrar != null) {
+                registrar.scheduleUpdate();
+            }
         } catch (RemoteException e) {
             // Ignore.
         }