Fixes projectiles being able to hit humans in organs they do not have.

Will also prevent body shields blocking bullets with non-existant limbs. Expands on the special return values for bullet_act(), adds defines for them.

code/game/objects/structures/girders.dm

@@ -25,7 +25,7 @@
 /obj/structure/girder/bullet_act(var/obj/item/projectile/Proj)
 	//Girders only provide partial cover. There's a chance that the projectiles will just pass through. (unless you are trying to shoot the girder)
 	if(Proj.original != src && !prob(cover))
-		return -1 //pass through
+		return PROJECTILE_CONTINUE //pass through
 
 	//Tasers and the like should not damage girders.
 	if(!(Proj.damage_type == BRUTE || Proj.damage_type == BURN))

code/game/objects/structures/grille.dm

@@ -94,7 +94,7 @@
 				passthrough = 1
 
 	if(passthrough)
-		. = -1
+		. = PROJECTILE_CONTINUE
 		damage = between(0, (damage - Proj.damage)*(Proj.damage_type == BRUTE? 0.4 : 1), 10) //if the bullet passes through then the grille avoids most of the damage
 
 	src.health -= damage*0.2