Merge pull request #6134 from Citadel-Station-13/upstream-merge-36230

[MIRROR] Pipenet fix

code/modules/atmospherics/machinery/datum_pipeline.dm

@@ -105,6 +105,8 @@
 		addMachineryMember(A)
 
 /datum/pipeline/proc/merge(datum/pipeline/E)
+	if(E == src)
+		return
 	air.volume += E.air.volume
 	members.Add(E.members)
 	for(var/obj/machinery/atmospherics/pipe/S in E.members)

code/modules/atmospherics/machinery/pipes/pipes.dm

@@ -79,9 +79,10 @@
 	parent = P
 
 /obj/machinery/atmospherics/pipe/Destroy()
+	QDEL_NULL(parent)
+
 	releaseAirToTurf()
-	qdel(air_temporary)
-	air_temporary = null
+	QDEL_NULL(air_temporary)
 
 	var/turf/T = loc
 	for(var/obj/machinery/meter/meter in T)
@@ -91,8 +92,6 @@
 			qdel(meter)
 	. = ..()
 
-	QDEL_NULL(parent)
-
 /obj/machinery/atmospherics/pipe/proc/update_node_icon()
 	for(var/i in 1 to device_type)
 		if(nodes[i])