Allow conditions to apply to all, except blacklisted entries

Currently, if you make a switch "selective" and then add a condition which excludes on thing (e.g. user/ip address) and add no other conditions, then one would assume that the switch will be active for all, *except* the user/ip address you explicitly blacklisted, and would be false for that user/ip address.

However this is not the case, instead the switch is not active for anyone.

This is from a bug in applying conditions. This patch fixes that.