Medias with no URI shouldn't be clickable
Migrated from https://bugzilla.gnome.org/show_bug.cgi?id=782367
Recently the way Media are built has been refactored and they can have 0..n URIs attached to them instead of 1. But with that comes a problem: the media selector allow to select medias with no associated URI, leading into seemingly freezing the PlayStation emulator.
We should prevent medias with no URI from being selected.