Skip calling set custom value if nothing has changed.

The call will trigger a setup of the local help manager,
which is rather heavy and should be avoided if possible.

Change-Id: I03fbe6a30fba6ac48361c7e2b5aa6d45dad5126b
Reviewed-by: Niels Weber <niels.2.weber@nokia.com>
Reviewed-by: Karsten Heimrich <karsten.heimrich@nokia.com>

src/plugins/help/generalsettingspage.h

@@ -79,6 +79,7 @@ private:
     QString m_homePage;
     int m_contextOption;
 
+    int m_startOption;
     bool m_returnOnClose;
 
     QString m_searchKeywords;