Fixes medical cyborgs being unable to interact with carbons (#3152)

<!-- Write **BELOW** The Headers and **ABOVE** The comments else it may
not be viewable. -->
<!-- You can view Contributing.MD for a detailed description of the pull
request process. -->

## About The Pull Request

Painkiller checks for cauterization now check the target rather than the
person applying treatmenrr. This has no player-facing effects outside
fixing a runtime preventing cyborgs from interacting with people

Robotic limbs will now always have healing prioritized over
cauterization if brute damage is present, since healing damage slows
bleeding

## Why It's Good For The Game

Uops :3

## Changelog

:cl:
fix: cyborgs can touch people again
code: robotic limbs will always have healing prioritized over being
cauterized if treated with a welder
/:cl:

<!-- Both :cl:'s are required for the changelog to work! You can put
your name to the right of the first :cl: if you want to overwrite your
GitHub username as author ingame. -->
<!-- You can use multiple of the same prefix (they're only used for the
icon ingame) and delete the unneeded ones. Despite some of the tags,
changelogs should generally represent how a player might be affected by
the changes rather than a summary of the PR's contents. -->

code/modules/mob/living/carbon/carbon_defense.dm

@@ -1,7 +1,7 @@
 /mob/living/carbon/attackby(obj/item/W, mob/user, params)
 	var/obj/item/bodypart/BP = get_bodypart(check_zone(user.zone_selected))
-	var/has_painkillers = user.reagents.has_reagent(/datum/reagent/medicine/morphine, needs_metabolizing = TRUE)
-	if(W.tool_behaviour == TOOL_WELDER && IS_ROBOTIC_LIMB(BP) && BP.brute_dam > 5) //prioritize healing if we're synthetic
+	var/has_painkillers = reagents.has_reagent(/datum/reagent/medicine/morphine, needs_metabolizing = TRUE)
+	if(W.tool_behaviour == TOOL_WELDER && IS_ROBOTIC_LIMB(BP) && BP.brute_dam) //prioritize healing if we're synthetic
 		return ..()
 	if(user.a_intent != INTENT_HELP || !W.get_temperature() || !BP.can_bandage()) //this will also catch low damage synthetic welding
 		return ..()