[test-ui] Fixed critical warning when trying to get contents from NULL GValue.
[test-ui] Fixed critical warning when trying to get contents
from NULL GValue.

kyoushuu/grilo,grilofw/grilo,grilofw/grilo,jasuarez/grilo,GNOME/grilo,grilofw/grilo,MathieuDuponchelle/grilo,jasuarez/grilo,MathieuDuponchelle/grilo,kyoushuu/grilo,jasuarez/grilo,MathieuDuponchelle/grilo,kyoushuu/grilo,kyoushuu/grilo,GNOME/grilo