Fix a monkey crash.

The monkey crashed because getTopWindow() returned null.
Ensure that we either have a top window, or we are in
the tab picker.  If neither is true, return false, to
avoid the null pointer exception.
diff --git a/src/com/android/browser/BrowserActivity.java b/src/com/android/browser/BrowserActivity.java
index 53814f2..3252da3 100644
--- a/src/com/android/browser/BrowserActivity.java
+++ b/src/com/android/browser/BrowserActivity.java
@@ -1387,6 +1387,9 @@
         mCanChord = true;
         int id = item.getItemId();
         final WebView webView = getTopWindow();
+        if (null == webView) {
+            return false;
+        }
         final HashMap hrefMap = new HashMap();
         hrefMap.put("webview", webView);
         final Message msg = mHandler.obtainMessage(
@@ -1442,6 +1445,9 @@
             // menu key.
             return false;
         }
+        if (null == mTabOverview && null == getTopWindow()) {
+            return false;
+        }
         switch (item.getItemId()) {
             // -- Main menu
             case R.id.goto_menu_id: {