Delegate QWebEngineHistory::currentItem() to itemAt()

Calling QWebEngineHistory::currentItem() before the first item is
inserted, caused a segfault, due to accessing an illegal QList index.
We now delegate the lookup to QWebEngineHistory::itemAt(), which checks
the index first and returns a dummy element in case of an illegal
index.

Task-number: QTBUG-59599
Change-Id: I9cdd2533e33415a7b812c29fff5429eb005020dc
Reviewed-by: Michael Brüning <michael.bruning@qt.io>

src/webenginewidgets/api/qwebenginehistory.cpp

@@ -226,9 +226,7 @@ QWebEngineHistoryItem QWebEngineHistory::backItem() const
 
 QWebEngineHistoryItem QWebEngineHistory::currentItem() const
 {
-    Q_D(const QWebEngineHistory);
-    d->updateItems();
-    return d->items[currentItemIndex()];
+    return itemAt(currentItemIndex());
 }
 
 QWebEngineHistoryItem QWebEngineHistory::forwardItem() const