Help: Workaround overrideCursor issue with WebEngine based viewer

QWebEngineViewer never sends a loadFinished signal (but a loadStarted
signal) when only the URL fragment changes (QTBUG-65223). Work around by
logging the last URL and recognizing that condition.

Task-number: QTCREATORBUG-19649
Change-Id: I7b96fe60f5c76ebffb36c23e8d62c6cb1aa515aa
Reviewed-by: Tobias Hunger <tobias.hunger@qt.io>

src/plugins/help/webenginehelpviewer.h

@@ -97,6 +97,7 @@ public:
 
 private:
     WebView *m_widget;
+    QUrl m_previousUrlWithoutFragment;
 };
 
 } // namespace Internal