Fixes hostile mob's friends list entries getting deleted while in use (#37297)

* Adds a check to ensure that the lastassailant weakref isn't also being used by a hostile mob for its friends list, preventing mobs from forgetting their friends.

* Replaces lastassailant weakref deletion with setting to null

Fixes bugs caused by the lastassailant weakref getting deleted, which would break any other objects that were using that weakref.

Author: noirogen

code/__HELPERS/logging.dm

@@ -95,7 +95,7 @@
 	if (ismob(target))
 		target.attack_log += text("\[[time_stamp()]\] <font color='orange'>Has been [what_done] by [user_txt][object_txt].[intent_txt][addition_txt]</font>")
 		if (!iscarbon(user))
-			QDEL_NULL(target.lastassailant)
+			target.lastassailant = null
 
 	if (ismob(user) && ismob(target))
 		target.assaulted_by(user)

code/modules/runescape/runescape_pvp.dm

@@ -59,7 +59,7 @@ var/list/non_standard_maint_areas = list(
 
 /mob/proc/assaulted_by(var/mob/M,var/weak_assault=FALSE)
 	if(!iscarbon(M))
-		QDEL_NULL(lastassailant)
+		lastassailant = null
 	else
 		lastassailant = makeweakref(M)