lua-factory: Warn when dates are in an invalid format
lua-factory: Warn when dates are in an invalid format

Instead of throwing g_date_time_unref() errors.

https://bugzilla.gnome.org/show_bug.cgi?id=739508

MathieuDuponchelle/grilo-plugins,GNOME/grilo-plugins,MathieuDuponchelle/grilo-plugins,jasuarez/grilo-plugins,grilofw/grilo-plugins,MikePetullo/grilo-plugins,MathieuDuponchelle/grilo-plugins,MikePetullo/grilo-plugins,GNOME/grilo-plugins,MikePetullo/grilo-plugins,MathieuDuponchelle/grilo-plugins,grilofw/grilo-plugins,jasuarez/grilo-plugins