Weighs misfire chances + sanitizes code (#4120)

## About The Pull Request

weighs misfire bodyzone chances

## Why It's Good For The Game

more mechanically interesting than #4119. more mechanically interesting
than prior system

## Changelog

:cl:
balance: misfire targetting is now weighed towards the legs
/:cl:

code/modules/projectiles/gun.dm

@@ -1011,15 +1011,16 @@
 		human_holder = src
 	for(var/obj/item/gun/at_risk in get_all_contents())
 		var/chance_to_fire = round(GUN_NO_SAFETY_MALFUNCTION_CHANCE_MEDIUM * at_risk.safety_multiplier)
+		var/bodyzone = pick_weight(list(BODY_ZONE_HEAD = 1, BODY_ZONE_CHEST = 9, BODY_ZONE_L_ARM = 4, BODY_ZONE_R_ARM = 4, BODY_ZONE_L_LEG = 41, BODY_ZONE_R_LEG = 41))
 		if(human_holder)
 			// gun is less likely to go off in a holster
 			if(at_risk == human_holder.s_store)
 				chance_to_fire = round(GUN_NO_SAFETY_MALFUNCTION_CHANCE_LOW * at_risk.safety_multiplier)
+				bodyzone = pick_weight(list(BODY_ZONE_CHEST = 10, BODY_ZONE_L_LEG = 45, BODY_ZONE_R_LEG = 45))
 		if(at_risk.safety == FALSE && prob(chance_to_fire))
-			var/bodyzone = pick(BODY_ZONE_HEAD, BODY_ZONE_CHEST, BODY_ZONE_L_ARM, BODY_ZONE_R_ARM, BODY_ZONE_L_LEG,BODY_ZONE_R_LEG)
 			if(at_risk.process_fire(src,src,FALSE, null, bodyzone) == TRUE)
 				log_combat(src,src,"misfired",at_risk,"caused by [cause]")
-				visible_message(span_danger("\The [at_risk.name]'s trigger gets caught as [src] falls, suddenly going off into [src]'s [bodyzone]!"), span_danger("\The [at_risk.name]'s trigger gets caught on something as you fall, suddenly going off into your [bodyzone]!"))
+				visible_message(span_danger("\The [at_risk.name]'s trigger gets caught as [src] falls, suddenly going off into [src]'s [get_bodypart(bodyzone)]!"), span_danger("\The [at_risk.name]'s trigger gets caught on something as you fall, suddenly going off into your [get_bodypart(bodyzone)]!"))
 				human_holder.force_scream()
 
 //I need to refactor this into an attachment