A few damage and defence related fixes

* Fixes projectiles still damaging suits even though completely blocked (blocked = 2) by a shield
* Fixes damage not causing dismemberment
* Fixes melee attacks always using area effect armour values, as def_zone is normally not set when attacking with a melee weapon, and the melee armour check didn't use target_zone for some reason. Now armor that only covers the chest will only protect the chest, instead of melee attacks using average armour all the time.