fixes welder tool using up fuel on clicks that produce no action (#3959)

# About the pull request

you no longer lose your precious fuel if you click on things that can't
be welded (you still lose fuel if you hit mobs)
also got rid of all 1 letter vars in the proc i touched
fixes #3776 

# Explain why it's good for the game

fix good


# Testing Photographs and Procedure
<details>
<summary>Screenshots & Videos</summary>

Put screenshots and videos here with an empty line between the
screenshots and the `<details>` tags.

</details>


# Changelog
:cl:Khadd
fix: blowtorch no longer loses fuel on clicks that produce no action
code: replaced 1-letter vars
/:cl:

code/game/objects/items/tools/maintenance_tools.dm

@@ -219,41 +219,43 @@
 		toggle(TRUE)
 
 
-/obj/item/tool/weldingtool/attack(mob/M, mob/user)
+/obj/item/tool/weldingtool/attack(mob/target, mob/user)
 
-	if(ishuman(M))
-		var/mob/living/carbon/human/H = M
-		var/obj/limb/S = H.get_limb(user.zone_selected)
+	if(ishuman(target))
+		var/mob/living/carbon/human/human = target
+		var/obj/limb/limb = human.get_limb(user.zone_selected)
 
-		if (!S) return
-		if(!(S.status & (LIMB_ROBOT|LIMB_SYNTHSKIN)) || user.a_intent != INTENT_HELP)
+		if (!limb) return
+		if(!(limb.status & (LIMB_ROBOT|LIMB_SYNTHSKIN)) || user.a_intent != INTENT_HELP)
 			return ..()
 
 		if(user.action_busy)
 			return
 		var/self_fixing = FALSE
 
-		if(H.species.flags & IS_SYNTHETIC && M == user)
+		if(human.species.flags & IS_SYNTHETIC && target == user)
 			self_fixing = TRUE
 
-		if(S.brute_dam && welding)
+		if(limb.brute_dam && welding)
 			remove_fuel(1,user)
 			if(self_fixing)
-				user.visible_message(SPAN_WARNING("\The [user] begins fixing some dents on their [S.display_name]."), \
-					SPAN_WARNING("You begin to carefully patch some dents on your [S.display_name] so as not to void your warranty."))
+				user.visible_message(SPAN_WARNING("\The [user] begins fixing some dents on their [limb.display_name]."), \
+					SPAN_WARNING("You begin to carefully patch some dents on your [limb.display_name] so as not to void your warranty."))
 				if(!do_after(user, 30, INTERRUPT_ALL, BUSY_ICON_FRIENDLY))
 					return
 
-			S.heal_damage(15, 0, TRUE)
-			H.pain.recalculate_pain()
-			H.UpdateDamageIcon()
-			user.visible_message(SPAN_WARNING("\The [user] patches some dents on \the [H]'s [S.display_name] with \the [src]."), \
-								SPAN_WARNING("You patch some dents on \the [H]'s [S.display_name] with \the [src]."))
+			limb.heal_damage(15, 0, TRUE)
+			human.pain.recalculate_pain()
+			human.UpdateDamageIcon()
+			user.visible_message(SPAN_WARNING("\The [user] patches some dents on \the [human]'s [limb.display_name] with \the [src]."), \
+								SPAN_WARNING("You patch some dents on \the [human]'s [limb.display_name] with \the [src]."))
 			return
 		else
 			to_chat(user, SPAN_WARNING("Nothing to fix!"))
 
 	else
+		if(ismob(target))
+			remove_fuel(1)
 		return ..()
 
 /obj/item/tool/weldingtool/afterattack(obj/target, mob/user, proximity)
@@ -274,8 +276,6 @@
 			tank.explode()
 		return
 	if (welding)
-		remove_fuel(1)
-
 		if(isliving(target))
 			var/mob/living/L = target
 			L.IgniteMob()