filechooserwidget: Create recent manager when setting operation mode

filechooserwidget: Create recent manager when setting operation mode

Creating a recent manager can be fairly expensive and we won't use it if
the widget is not visible or the recent mode has not been entered. Code
other places can already handle a NULL recent manager, so just create it
when entering the recent mode. And shove 25ms of startup time off the
widget-factory this way.