python: add trivial error handling to grilo-test-ui
python: add trivial error handling to grilo-test-ui

Some trivial error handling is added to Python's grilo-test-ui
since currently these functions can throw an exception.

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