Wrong spawn protection area check

So, it's simple. Find spawn protection border and click on the ground. You can't place block. Now click on side block near area and block will be placed into it. Can be fixed by checking not only the clicked block, but also block on clicked side. But, please, with CASE (not IF-ELSE IF).
Why that bug is so important? Some players can build undestroyable wall around spawn on vanilla servers. It would be not very cool.