Fix action bar items missing when opening new message.

Calling configureMenu() inside updateMenu() doesn't update the
buttons properly. Instead, call invalidateOptionsMenu(). This forces
the menu to be re-created, and onPreareOptionsMenu() to be called.
From there, configureMenu() is called automatically.

src/com/fsck/k9/activity/MessageList.java

@@ -1347,7 +1347,7 @@ public class MessageList extends K9FragmentActivity implements MessageListFragme
 
     @Override
     public void updateMenu() {
-        configureMenu(mMenu);
+        invalidateOptionsMenu();
     }
 
     @Override