ZNC 1.4 never had certificate validation. That feature was added in ZNC 1.6. Therefore you are asking for a new feature or item to be added, so the bug is a Wishlist type bug.
I would be extremely wary of incorporating this change into 1.4's packaging if only due to the fact that you haven't tested if it cleanly applies. It may in fact be dependent on CSocket changes or others so I would hesitate to add this functionality to a version that wasn't designed with that feature in mind. (Patrick gets the final say in the matter, though if you want 1.6 features in Jessie I would consider compiling yourself, or use an available third party repository as referred to on ZNC upstream's Installation documentation - http://wiki.znc.in/Installation#Debian )
