Do not feed the monkey

     Bug: 5261282

Change-Id: I8c982436e9fb45e6d79afe0a6294389d626b6276
diff --git a/src/com/android/browser/NavigationBarTablet.java b/src/com/android/browser/NavigationBarTablet.java
index 661ed71..c22b1a0 100644
--- a/src/com/android/browser/NavigationBarTablet.java
+++ b/src/com/android/browser/NavigationBarTablet.java
@@ -249,6 +249,7 @@
     }
 
     private void stopOrRefresh() {
+        if (mUiController == null) return;
         if (mTitleBar.isInLoad()) {
             mUiController.stopLoading();
         } else {