[MIRROR] Fixes minor logging issue with hydroponics trays (#2922)

* Fixes minor logging issue with hydroponics trays (#56381)

Hydroponics trays have a var, lastuser, that it's supposed to use in logging as the last person who modified a tray's reagents
this variable was only set if you transferred reagents to the tray via composting, so it was null 99% of the time.

The var is now set when any reagents are transferred and the logging for spawning spiders now uses this var.

The var is now a weakref, to prevent hydroponics trays from harddels.

"null last modified a tray's contents that spawned spiderlings." Not very helpful to admins, is it.

* Fixes minor logging issue with hydroponics trays

Co-authored-by: MrMelbert <51863163+MrMelbert@users.noreply.github.com>

code/modules/hydroponics/hydroponics.dm

@@ -49,7 +49,7 @@
 	///Have we been visited by a bee recently, so bees dont overpollinate one plant
 	var/recent_bee_visit = FALSE
 	///The last user to add a reagent to the tray, mostly for logging purposes.
-	var/mob/lastuser
+	var/datum/weakref/lastuser
 	///If the tray generates nutrients and water on its own
 	var/self_sustaining = FALSE
 
@@ -153,7 +153,7 @@
 
 //Nutrients//////////////////////////////////////////////////////////////
 			// Nutrients deplete at a constant rate, since new nutrients can boost stats far easier.
-			apply_chemicals(lastuser)
+			apply_chemicals(lastuser?.resolve())
 			if(self_sustaining)
 				reagents.remove_any(min(0.5, nutridrain))
 			else
@@ -567,9 +567,9 @@
 				H.adjustWater(round(water_amt))
 				reagent_source.reagents.remove_reagent(/datum/reagent/water, water_amt)
 			reagent_source.reagents.trans_to(H.reagents, transfer_amount, transfered_by = user)
+			lastuser = WEAKREF(user)
 			if(IS_EDIBLE(reagent_source) || istype(reagent_source, /obj/item/reagent_containers/pill))
 				qdel(reagent_source)
-				lastuser = user
 				H.update_icon()
 				return 1
 			H.update_icon()