Fix NPE if FPE service does not exist.

Bug: 19846662
Change-Id: I44e014c66a524b282cce0cfc9b7513fc0f553576
diff --git a/services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java b/services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java
index 40e2056..ec1258c 100644
--- a/services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java
+++ b/services/devicepolicy/java/com/android/server/devicepolicy/DevicePolicyManagerService.java
@@ -3031,7 +3031,9 @@
                     }
                     PersistentDataBlockManager manager = (PersistentDataBlockManager)
                             mContext.getSystemService(Context.PERSISTENT_DATA_BLOCK_SERVICE);
-                    manager.wipe();
+                    if (manager != null) {
+                        manager.wipe();
+                    }
                 }
                 boolean wipeExtRequested = (flags & WIPE_EXTERNAL_STORAGE) != 0;
                 wipeDeviceOrUserLocked(wipeExtRequested, userHandle,