Fix some crashes in launcher2.

http://b/issue?id=2142064
diff --git a/src/com/android/launcher2/DeferredHandler.java b/src/com/android/launcher2/DeferredHandler.java
index 433bf55..ce60352 100644
--- a/src/com/android/launcher2/DeferredHandler.java
+++ b/src/com/android/launcher2/DeferredHandler.java
@@ -40,6 +40,9 @@
         public void handleMessage(Message msg) {
             Runnable r;
             synchronized (mQueue) {
+                if (mQueue.size() == 0) {
+                    return;
+                }
                 r = mQueue.removeFirst();
             }
             r.run();