Fix NPE in AppOpsService

bug:22802981

Change-Id: I73eee5ff9cf1603d8f30355554ef075aa14afd30
diff --git a/services/core/java/com/android/server/AppOpsService.java b/services/core/java/com/android/server/AppOpsService.java
index ec02789..2a3492b 100644
--- a/services/core/java/com/android/server/AppOpsService.java
+++ b/services/core/java/com/android/server/AppOpsService.java
@@ -1718,11 +1718,15 @@
     }
 
     private static String[] getPackagesForUid(int uid) {
+        String[] packageNames = null;
         try {
-            return AppGlobals.getPackageManager().getPackagesForUid(uid);
+            packageNames= AppGlobals.getPackageManager().getPackagesForUid(uid);
         } catch (RemoteException e) {
             /* ignore - local call */
         }
-        return EmptyArray.STRING;
+        if (packageNames == null) {
+            return EmptyArray.STRING;
+        }
+        return packageNames;
     }
 }