Don't allow ventcrawling if vents are welded

What's the point of welding vents, again?

code/modules/ventcrawl/ventcrawl_atmospherics.dm

@@ -55,6 +55,12 @@
 /obj/machinery/atmospherics/proc/can_crawl_through()
 	return 1
 
+/obj/machinery/atmospherics/unary/can_crawl_through()
+	if(welded)
+		return 0
+
+	..()
+
 /obj/machinery/atmospherics/proc/findConnecting(var/direction)
 	for(var/obj/machinery/atmospherics/target in get_step(src,direction))
 		if(target.initialize_directions & get_dir(target,src))