Core: Actually create settings widget

Amends dae9cb13cf

Change-Id: I0f4bef0b84e3383860ac5d871dabf089badbcf11
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/coreplugin/systemsettings.cpp

@@ -263,6 +263,7 @@ SystemSettings::SystemSettings()
     setId(Constants::SETTINGS_ID_SYSTEM);
     setDisplayName(tr("System"));
     setCategory(Constants::SETTINGS_CATEGORY_CORE);
+    setWidgetCreator([] { return new SystemSettingsWidget; });
 }
 
 } // namespace Internal