Browser: Ignore title updates when history has no current item

The Browser::History class is oblivious to the state of the browsing
context's session history over on the LibWeb side. We need to hook a lot
more thing up here, but for now just ignore updates when there's no
current history item. This fixes a VERIFY() error on startup.

Userland/Applications/Browser/History.cpp

@@ -57,6 +57,8 @@ void History::clear()
 
 void History::update_title(String const& title)
 {
+    if (m_current == -1)
+        return;
     m_items[m_current].title = title;
 }