Fixes spurious failures in pipe icon generation (#14585)

code/controllers/subsystem/air.dm

@@ -39,6 +39,9 @@ SUBSYSTEM_DEF(air)
 	var/list/active_super_conductivity = list()
 	var/list/high_pressure_delta = list()
 
+	/// Pipe overlay/underlay icon manager
+	var/datum/pipe_icon_manager/icon_manager
+
 
 	var/list/currentrun = list()
 	var/currentpart = SSAIR_DEFERREDPIPENETS
@@ -66,6 +69,7 @@ SUBSYSTEM_DEF(air)
 
 /datum/controller/subsystem/air/Initialize(timeofday)
 	setup_overlays() // Assign icons and such for gas-turf-overlays
+	icon_manager = new() // Sets up icon manager for pipes
 	setup_allturfs()
 	setup_atmos_machinery(GLOB.machines)
 	setup_pipenets(GLOB.machines)