Missing icons on the settings dialog's buttons.

[Jasper Huijsmans]

...
> No, the strange thing is :
> /usr/share/icons/hicolor/48x48/apps/xfce4-workspaces.svg
> /usr/share/icons/hicolor/48x48/apps/xfwm4.svg
> 
> .svg icons in 48x48 subdir.
> 

Fixed. Thanks ;-)