Avoid NPE when template rapidly switched.

Monkeys can race and end up swapping template before the dialog
is shown.

Bug: 16660160
Change-Id: I301784d707ee3998c38cf2874f7016a5c5350825
diff --git a/src/com/android/settings/DataUsageSummary.java b/src/com/android/settings/DataUsageSummary.java
index ec52128..009c758 100644
--- a/src/com/android/settings/DataUsageSummary.java
+++ b/src/com/android/settings/DataUsageSummary.java
@@ -1791,10 +1791,12 @@
         public static void show(DataUsageSummary parent) {
             if (!parent.isAdded()) return;
 
+            final NetworkPolicy policy = parent.mPolicyEditor.getPolicy(parent.mTemplate);
+            if (policy == null) return;
+
             final Resources res = parent.getResources();
             final CharSequence message;
-            final long minLimitBytes = (long) (
-                    parent.mPolicyEditor.getPolicy(parent.mTemplate).warningBytes * 1.2f);
+            final long minLimitBytes = (long) (policy.warningBytes * 1.2f);
             final long limitBytes;
 
             // TODO: customize default limits based on network template