Fix NPE

Bug: 7371837
diff --git a/src/com/android/launcher2/Launcher.java b/src/com/android/launcher2/Launcher.java
index 6fcda8a..2c5f2b5 100644
--- a/src/com/android/launcher2/Launcher.java
+++ b/src/com/android/launcher2/Launcher.java
@@ -3482,7 +3482,9 @@
             anim.addListener(new AnimatorListenerAdapter() {
                 @Override
                 public void onAnimationEnd(Animator animation) {
-                    mWorkspace.postDelayed(mBuildLayersRunnable, 500);
+                    if (mWorkspace != null) {
+                        mWorkspace.postDelayed(mBuildLayersRunnable, 500);
+                    }
                 }
             });
             anim.start();