Help: Fix that context help does not end up with focus

When opening a help url with anchor for context help, the help viewer
would loose focus, breaking behavior like pressing F1 twice to go to
help mode.

Task-number: QTCREATORBUG-9093
Change-Id: Ib6b6ecb4f6bec63f545c1f4ff973d878547f3ee1
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/coreplugin/rightpane.cpp

@@ -145,6 +145,8 @@ RightPaneWidget *RightPaneWidget::instance()
 
 void RightPaneWidget::setWidget(QWidget *widget)
 {
+    if (widget == m_widget)
+        return;
     clearWidget();
     m_widget = widget;
     if (m_widget) {