Gio::SettingsSchemaSource: do an extra reference() for returning value
Gio::SettingsSchemaSource: do an extra reference() for returning value

    * gio/src/settingsschemasource.hg: method get_default() returns
      transfer-none value, what means that we need to increase refcount
      before wrapping the pointer by RefPtr class.

https://bugzilla.gnome.org/show_bug.cgi?id=774593

GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm,GNOME/glibmm