[MIRROR] Turf weakref persists in changeturf / Fix plasma cutters (#2209

)

* Turf weakref persists in changeturf / Fix plasma cutters  (#82906)

## About The Pull Request

Turf references don't change so logically, turf weakrefs wouldn't change
if the turf changes.

By not doing this this can cause bugs: See #82886 . (This Fixes #82886) 

(Projectiles hold a list of weakrefs to atoms hit to determine what they
have already hit.

Because turf weakrefs reset, we could "hit" the same turf twice if it
destroyed the turf.

Old behavior - this was fine but now that they're weakrefs, we get two
weakref datums in the list that point to the same ref.)

Less hacky alternative to #82901 . (Closes #82901) 

## Changelog

:cl: Melbert
fix: Plasma cutters work again
/:cl:

* Turf weakref persists in changeturf / Fix plasma cutters

---------

Co-authored-by: MrMelbert <[email protected]>

code/game/turfs/change_turf.dm

@@ -96,6 +96,8 @@ GLOBAL_LIST_INIT(blacklisted_automated_baseturfs, typecacheof(list(
 
 	var/list/old_baseturfs = baseturfs
 	var/old_type = type
+	var/datum/weakref/old_ref = weak_reference
+	weak_reference = null
 
 	var/list/post_change_callbacks = list()
 	SEND_SIGNAL(src, COMSIG_TURF_CHANGE, path, new_baseturfs, flags, post_change_callbacks)
@@ -142,6 +144,8 @@ GLOBAL_LIST_INIT(blacklisted_automated_baseturfs, typecacheof(list(
 
 	lattice_underneath = old_lattice_underneath
 
+	new_turf.weak_reference = old_ref
+
 	if(SSlighting.initialized)
 		// Space tiles should never have lighting objects
 		if(!space_lit)

code/modules/projectiles/projectile.dm

@@ -1205,7 +1205,6 @@
 	var/turf/startloc = get_turf(src)
 	var/obj/projectile/bullet = new projectile_type(startloc)
 	bullet.starting = startloc
-	var/list/ignore = list()
 	for (var/atom/thing as anything in ignore_targets)
 		bullet.impacted[WEAKREF(thing)] = TRUE
 	bullet.firer = firer || src