Don't crash in onDestroy.  Not all ApplicationInfos have their icons loaded.
diff --git a/src/com/android/launcher2/AppInfoCache.java b/src/com/android/launcher2/AppInfoCache.java
index 65ae570..f89e3ab 100644
--- a/src/com/android/launcher2/AppInfoCache.java
+++ b/src/com/android/launcher2/AppInfoCache.java
@@ -148,7 +148,9 @@
     public static void unbindDrawables() {
         synchronized (sCache) {
             for (ApplicationInfo appInfo: sCache.values()) {
-                appInfo.icon.setCallback(null);
+                if (appInfo.icon != null) {
+                    appInfo.icon.setCallback(null);
+                }
             }
         }
     }