Fixes delta damage calculation for organs (and brain getting traumas not from damage, but from mannitol healing) (#95103)

Co-authored-by: SmArtKar <44720187+SmArtKar@users.noreply.github.com>

code/modules/mob/living/brain/brain_item.dm

@@ -356,8 +356,8 @@
 	var/delta_dam = . //for the sake of clarity
 	if(isnull(bodypart_owner)) // no need to color it if it's in someone's noggin
 		update_brain_color()
-	if(delta_dam > 0 && damage > BRAIN_DAMAGE_MILD)
-		roll_for_brain_trauma(delta_dam)
+	if(delta_dam < 0 && damage > BRAIN_DAMAGE_MILD)
+		roll_for_brain_trauma(-delta_dam) // parent call returns negative numbers if take damage and positive if we heal
 
 /// Rolls a random chance to gain a brain trauma based on damage taken and current damage level
 /obj/item/organ/brain/proc/roll_for_brain_trauma(delta_dam)

code/modules/surgery/organs/internal/stomach/_stomach.dm

@@ -467,8 +467,8 @@
 /obj/item/organ/stomach/apply_organ_damage(damage_amount, maximum, required_organ_flag)
 	. = ..()
 	// So after a while, or a bunch of stomach meds, even a cut stomach can recover
-	if (. < 0)
-		cut_open_damage = max(0, cut_open_damage + .)
+	if (. > 0)
+		cut_open_damage = max(0, cut_open_damage - .)
 
 /obj/item/organ/stomach/examine(mob/user)
 	. = ..()