Fixes pipelines and their gas_mixtures hard deleting (#27551)

* WIP

* Now it works, I think

code/ATMOSPHERICS/datum_pipe_network.dm

@@ -17,13 +17,28 @@
 	..()
 
 /datum/pipe_network/Destroy()
+	if(line_members)
 		for(var/datum/pipeline/pipeline in line_members) //This will remove the pipeline references for us
 			pipeline.network = null
 		line_members = null
+
+	if(normal_members)
 		for(var/obj/machinery/atmospherics/objects in normal_members) //Procs for the different bases will remove the references
 			objects.unassign_network(src)
 		normal_members = null
+
 	pipe_networks -= src
+
+	if(air_transient)
+		qdel(air_transient)
+		air_transient = null
+
+	if(radiate)
+		qdel(radiate)
+		radiate = null
+
+	gases = null
+
 	..()
 
 /datum/pipe_network/proc/process()
@@ -73,6 +88,9 @@
 	for(var/datum/pipeline/line_member in giver.line_members)
 		line_member.network = src
 
+	giver.line_members = null
+	giver.normal_members = null
+	qdel(giver)
 
 	update_network_gases()
 	return 1

code/ATMOSPHERICS/datum_pipeline.dm

@@ -15,7 +15,8 @@
 	if(network) //For the pipenet rebuild
 		qdel(network)
 		network = null
-	if(air && air.volume) //For the pipeline rebuild next tick
+	if(air) //For the pipeline rebuild next tick
+		if(air.total_moles)
 			temporarily_store_air()
 		qdel(air)
 		air = null
@@ -101,9 +102,12 @@
 /datum/pipeline/proc/network_expand(datum/pipe_network/new_network, obj/machinery/atmospherics/pipe/reference)
 
 
-	if(new_network.line_members.Find(src))
+	if(src in new_network.line_members)
 		return 0
 
+	if(network && (network != new_network))
+		return new_network.merge(network)
+
 	new_network.line_members += src
 
 	network = new_network