Don't crash on null Vibrator during reboot.

Bug: 3099305
Change-Id: I9af126f7a719f36ae544f517a2fccd0d33339389
diff --git a/core/java/com/android/internal/app/ShutdownThread.java b/core/java/com/android/internal/app/ShutdownThread.java
index 714b259..1fcd654 100644
--- a/core/java/com/android/internal/app/ShutdownThread.java
+++ b/core/java/com/android/internal/app/ShutdownThread.java
@@ -364,7 +364,7 @@
             // vibrator is asynchronous so we need to wait to avoid shutting down too soon.
             try {
                 Thread.sleep(SHUTDOWN_VIBRATE_MS);
-            } catch (InterruptedException e) {
+            } catch (InterruptedException unused) {
             }
         }