title-clip: Return default GESTitleSource value if no child set yet
In get_property we should return the default values if we have not created any GESTitleSource yet (instead of segfaulting). And fix GESTitleSource default values! Reviewed-by:Thibault Saunier <thibault.saunier@collabora.com> Differential Revision: https://phabricator.freedesktop.org/D737