XMDS: protect against an entirely empty default layout id. xibosignage/xibo#2779
XMDS: protect against an entirely empty default layout id. xibosignage/xibo#2779

dasgarner/xibo-cms,xibosignage/xibo-cms,dasgarner/xibo-cms,dasgarner/xibo-cms,xibosignage/xibo-cms,xibosignage/xibo-cms,xibosignage/xibo-cms,dasgarner/xibo-cms,xibosignage/xibo-cms,dasgarner/xibo-cms,dasgarner/xibo-cms,xibosignage/xibo-cms