Fix IllegalStateException in HistoryPage

 Bug: 3228114
 Fixes an IllegalStateException caused by the HistoryAdapter and
 the most visited cursor.

Change-Id: I85208448f7af82c382be8be9450730420ce51b7a
diff --git a/src/com/android/browser/BrowserHistoryPage.java b/src/com/android/browser/BrowserHistoryPage.java
index a3ce0b4..5cd9545 100644
--- a/src/com/android/browser/BrowserHistoryPage.java
+++ b/src/com/android/browser/BrowserHistoryPage.java
@@ -366,7 +366,10 @@
                 mMostVisited.close();
             }
             mMostVisited = cursor;
-            mMostVisited.registerDataSetObserver(mDataSetObserver);
+            if (mMostVisited != null) {
+                mMostVisited.registerDataSetObserver(mDataSetObserver);
+            }
+            notifyDataSetChanged();
         }
 
         @Override