Do not call gtk_tree_model_filter_set_visible_func() multiple times
Do not call gtk_tree_model_filter_set_visible_func() multiple times

Since there is no need to set the visible function more than once, do
it only once. This fixes some critical warnings.

community-ssu/hildon,archlinuxarm-n900/libhildon,community-ssu/hildon,archlinuxarm-n900/libhildon,archlinuxarm-n900/libhildon,community-ssu/hildon