gio/tests/task: Ensure that g_task_had_error doesn't forget the error
gio/tests/task: Ensure that g_task_had_error doesn't forget the error

https://bugzilla.gnome.org/show_bug.cgi?id=764163

johne53/MB3Glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,endlessm/glib,endlessm/glib,johne53/MB3Glib,endlessm/glib,johne53/MB3Glib,johne53/MB3Glib,johne53/MB3Glib