Only set the visible func in the filter if necessary
Only set the visible func in the filter if necessary

This avoids overriding a visible function set by the user directly
in the model filter.

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